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pro·tein (p),

(prō'tēn, prōo'tē-in), Do not confuse this word with protean.
Macromolecules consisting of long sequences of α-amino acids [H2N-CHR-COOH] in peptide (amide) linkage (elimination of H2O between the α-NH2 and α-COOH of successive residues). Protein is three fourths of the dry weight of most cell matter and is involved in structures, hormones, enzymes, muscle contraction, immunologic response, and essential life functions. The amino acids involved are generally the 20 α-amino acids (for example, glycine, l-alanine) recognized by the genetic code. Crosslinks yielding globular forms of protein are often effected through the -SH groups of two l-cysteinyl residues, as well as by noncovalent forces (hydrogen bonds, lipophilic attractions, etc.).
[G. prōtos, first, + -in]


/pro·tein/ (pro´tēn) any of a group of complex organic compounds containing carbon, hydrogen, oxygen, nitrogen, and sulfur. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist of α-amino acids joined by peptide linkages. Twenty different amino acids are commonly found in proteins, each protein having a unique, genetically defined amino acid sequence that determines its specific shape and function. Their roles include enzymatic catalysis, transport and storage, coordinated motion, nerve impulse generation and transmission, control of growth and differentiation, immunity, and mechanical suppport.
AA protein  see under amyloid.
acute phase protein  any of the non-antibody proteins found in increased amounts in serum during the acute phase response, including C-reactive protein and fibrinogen.
AL protein  see under amyloid.
amyloid A protein  AA amyloid.
amyloid light chain protein  AL amyloid.
amyloid precursor protein  (APP) a large transmembrane glycoprotein expressed on the cell surface and of uncertain function; endocytosis and cleavage can produce abnormal 40 to 43 amino acid peptides which aggregate to form A, associated with Alzheimer's disease.
Bence Jones protein  a low-molecular-weight, heat-sensitive urinary protein found in multiple myeloma, which coagulates when heated to 45°–55°C and redissolves partially or wholly on boiling.
binding protein 
1. any protein able to specifically and reversibly bind other substances, such as ions, sugars, nucleic acids, or amino acids; they are believed to function in transport.
protein C  a vitamin K–dependent plasma protein that, when activated by thrombin, inhibits the clotting cascade by enzymatic cleavage of factors V and VIII and also enhances fibrinolysis. Deficiency results in recurrent venous thrombosis.
C4 binding protein  a complement system regulatory protein that inhibits activation of the classical pathway.
complete protein  one containing the essential amino acids in the proportion required in the human diet.
compound protein , conjugated protein any of those in which the protein is combined with nonprotein molecules or prosthetic groups other than as a salt; e.g., nucleoproteins, glycoproteins, lipoproteins, and metalloproteins.
C-reactive protein  a globulin that forms a precipitate with the C-polysaccharide of the pneumonococcus; the most predominant of the acute phase proteins.
cystic fibrosis transmembrane regulator protein  a transmembrane protein produced by the cystic fibrosis gene, primarily functioning as a chloride channel. Numerous mutated forms of the gene have been associated with clinical cystic fibrosis.
fibrillar protein  any of the generally insoluble proteins that comprise the principal structural proteins of the body, e.g., collagens, elastins, keratin, actin, and myosin.
G protein  any of a family of proteins of the intracellular portion of the plasma membrane that bind activated receptor complexes and, through conformational changes and cyclic binding and hydrolysis of GTP, effect alterations in channel gating and so couple cell surface receptors to intracellular responses.
glial fibrillary acidic protein  (GFAP) the protein forming the glial filaments of the astrocytes and used as an immunohistochemical marker of these cells.
globular protein  any of the water-soluble proteins yielding only α-amino acids on hydrolysis, including most of the proteins of the body, e.g., albumins and globulins.
guanyl-nucleotide-binding protein  G p.
heat shock protein  any of a group of proteins first identified as synthesized in response to hyperthermia, hypoxia, or other stresses and believed to enable cells to recover from these stresses. Many have been found to be molecular chaperones and are synthesized abundantly regardless of stress.
HIV proteins  proteins specific to the human immunodeficiency virus; presence of certain specific HIV proteins together with certain HIV glycoproteins constitutes a serological diagnosis of HIV infection.
incomplete protein  one having a ratio of essential amino acids different from that of the average body protein.
membrane cofactor protein  (MCP) an inhibitor of complement activation found in most blood cells, endothelial and epithelial cells, and fibroblasts.
myeloma protein  any of the abnormal immunoglobulins or fragments, such as Bence-Jones proteins, secreted by myeloma cells.
partial protein  incomplete p.
plasma proteins  all the proteins present in the blood plasma, including the immunoglobulins.
prion protein  (PrP) a protein of uncertain function, in humans coded for by a gene on the short arm of chromosome 20. The protease-resistant core is the functional, and perhaps only, component of prions; several abnormal forms have been identified and are responsible for prion disease.
protein S  a vitamin K–dependent plasma protein that inhibits blood clotting by serving as a cofactor for activated protein C.
S protein  see vitronectin.
SAA protein  serum amyloid A p.
serum proteins  proteins in the blood serum, including immunoglobulins, albumin, complement, coagulation factors, and enzymes.
serum amyloid A protein  SAA p.; a high-molecular-weight protein synthesized in the liver; it is an acute phase protein and circulates in association with HDL lipoprotein. It is the precursor to AA amyloid and accumulates in inflammation.
sphingolipid activator protein  (SAP) any of a group of non-enzymatic lysosomal proteins that stimulate the actions of specific lysosomal hydrolases by binding and solubilizing their sphingolipid substrates.
transport protein  a protein that binds to a substance and provides a transport system for it, either in the plasma or across a plasma membrane.


(prō′tēn′, -tē-ĭn)
Any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism. They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.

pro′tein·a′ceous (prōt′n-ā′shəs, prō′tē-nā′-), pro·tein′ic (prō-tē′nĭk)(prō-tē′nəs), pro·tein′ous (prō-tē′nəs) adj.


[prō′tē·in, prō′tēn]
Etymology: Gk, proteios, first rank
any of a large group of naturally occurring complex organic nitrogenous compounds. Each is composed of large combinations of amino acids (usually 50 or more) containing the elements carbon, hydrogen, nitrogen, oxygen, and occasionally sulfur, phosphorus, iron, iodine, or other essential constituents of living cells. Twenty-two amino acids have been identified as vital for proper growth, development, and maintenance of health. The body can synthesize 13 of these, the nonessential amino acids, whereas the remaining 9 must be obtained from dietary sources and are termed essential. Protein is the major source of building material for muscles, blood, skin, hair, nails, and the internal organs. It is necessary for the formation of many hormones, enzymes, and antibodies and may act as a source of energy. Rich dietary sources are meat, poultry, fish, eggs, milk, and cheese, which are classified as complete proteins because they contain the nine essential amino acids. Nuts and legumes, including navy beans, chickpeas, soybeans, and split peas, are also good sources but are incomplete proteins because they do not contain all the essential amino acids in adequate amounts. Protein deficiency causes abnormal growth and tissue development in children, leading to kwashiorkor, whereas in adults it results in lack of vigor and stamina, weakness, mental depression, poor resistance to infection, impaired healing of wounds, and slow recovery from disease. Excessive intake of protein may in some conditions result in fluid imbalance.

protein/creatinine ratio

the ratio of protein to creatinine in the urine, calculated as a measure of proteinuria.


Biochemistry A large molecule consisting of a long chain or sequence of amino acids with a general formula of H2N–CHR–COOH–aka alpha amino acids, joined in a peptide likage; after water, proteins are the major cell constituent, and are critical for all biological structures–eg, organelles, mitochondria, enzymes and functions–eg, growth, development, immune function, motility Types Hormones, enzymes, antibodies


Macromolecules consisting of long sequences of α-amino acids [H2N-CHR-COOH] in peptide (amide) linkage (elimination of H2O between the α-NH2 and α-COOH of successive residues). Protein is three fourths of the dry weight of most cell matter and is involved in structures, hormones, enzymes, muscle contraction, immunologic response, and essential life functions. The amino acids involved are generally the 20 α-amino acids (glycine, l-alanine) recognized by the genetic code. Cross-links yielding globular forms of protein are often effected through the -SH groups of two sulfur-containing l-cysteinyl residues, as well as by noncovalent forces (e.g., hydrogen bonds, lipophilic attractions).
Compare: bioregulator
[G. prōtos, first, + -in]


a large complex molecule (M W from 10 000 to more than 1 million) built up from AMINO ACIDS joined together by PEPTIDE BONDS. All proteins contain carbon, hydrogen, oxygen and nitrogen and most contain sulphur. Proteins are produced in the cytoplasm at the ribosomes (see PROTEIN SYNTHESIS and begin as long, unbranched POLYPEPTIDE CHAINS, the primary structure. All protein molecules undergo a physical rearrangement to give a secondary structure. The most common type of shape is alpha-helix (right-handed) where the coils are held in place by hydrogen bonds. Some proteins, such as keratin, remain at this stage. An alternative secondary structure is beta-pleatingwhere parallel polypeptide chains are cross-linked by hydrogen bonds forming an extremely tough structure, as in silk. Proteins with these relatively simple two-dimensional secondary structures are called fibrous proteins.

Some proteins undergo even more complex folding, where the secondary structure is arranged into a three-dimensional tertiary structure forming ‘globular’ proteins held together by forces between side groups. Such molecules are, for example, ENZYMES, ANTIBODIES, most blood proteins, and MYOGLOBIN. finally, globular proteins can be composed of two or more polypeptide chains loosely bonded together, for example, HAEMOGLOBIN, giving a quaternary structure.


A substance produced by a gene that is involved in creating the traits of the human body, such as hair and eye color, or is involved in controlling the basic functions of the human body, such as control of the cell cycle.


Complex organic molecule composed of various combinations of any of twenty α-amino acids linked in a genetically controlled linear sequence into one or more peptide chains. Proteins are present in every living cell and form an essential constituent of cells. They are essential in many functions, such as growth and repair of tissue, transport of molecules throughout the body (e.g. haemoglobin to carry oxygen), as enzymes to catalyse biochemical reactions, immunological responses, muscle contraction (with actin and myosin), signalling (e.g. insulin which transmits a signal from a cell where it is synthesized to other cells in other tissues), or as antibodies by binding to target receptors. Many of the twenty amino acids are produced by the body. However, nine of these have to be obtained in food.


Macromolecules consisting of long sequences of α-amino acids; represents three fourths of dry weight of most cell matter; involved in structures, hormones, enzymes, muscle contraction, immunologic response, and essential life functions.
[G. prōtos, first, + -in]


any large organic compound made from one or more polypeptides, which are chains of amino acids joined in a genetically determined order by peptide linkages between the carboxyl group of one amino acid and the amino group of the next. They contain carbon, hydrogen, oxygen and nitrogen and usually sulfur, occasionally phosphorus.
Proteins form a large and essential part of the body mass, comprising especially cell membranes, connective tissue, muscles, enzymes, hormones, blood proteins. To maintain this mass the diet must contain a high proportion of protein, especially in growing animals and those recovering from debilitating diseases.

protein A
a surface protein of Staphylococus aureus which binds to the Fc region of some IgG molecules. Fluorochrome-labeled protein A is used in an indirect immunofluorescence test for detecting bound immunoglobulins.
authentic protein
a recombinant protein with all its naturally occurring properties.
available protein
the portion of dietary protein that can be used by the animal.
protein binding
a property of many drugs which limits their distribution and availability in the blood, as well as affecting elimination from the body.
protein bumps
see bumps.
protein C
a circulating vitamin K-dependent protein with anticoagulant effects. Promotes fibrinolysis.
calories derived from proteins in the diet.
protein calorie malnutrition
inadequate protein in the diet leads to impaired cell-mediated immunity, delayed wound healing and loss of lean body mass.
protein-calorie ratio
the number of calories provided from protein sources, compared with the total caloric intake; an indication of the level of protein intake.
carrier protein
one which, when coupled to a hapten, renders it capable of eliciting an immune response.
complete protein
one containing the essential amino acids in the proportion required in the diet.
protein concentrates
feeds containing a high concentration of protein, e.g. legume grains and forages, meat meal, fish meal, oil cakes, milling residues including bran, shorts, middlings, brewer's grains.
conjugated p's
those in which the protein molecule is united with nonprotein molecules or prosthetic groups, e.g. glycoproteins, lipoproteins and metalloproteins.
protein-creatinine ratio
in urine is valuable in correcting for variation in urine contents due to variable dilutions.
crude protein
the total nitrogen content of a feed multiplied by 6.25. Includes several obvious errors but is still a close approximation of the protein content.
dietary protein
is usually the most expensive part of the diet, except for animals at pasture, and the constituent most likely to be deficient. An excess of protein in the diet in ruminants can cause a sharp rise in alkalinity, due to the release of ammonia, of the ruminal contents causing ruminal atony and indigestion.
digestible protein
the crude protein ingested less the protein excreted in the feces. The estimation requires a digestibility trial involving animals.
protein equivalent
said of a feed. The total nitrogen content expressed as protein if it were all in that form. That is the percentage nitrogen in the feed multiplied by the average percentage of nitrogen in plant protein (6.25%).
protein excretion t
one that uses 51Cr-labeled protein which measures protein excretion in the feces in cases of protein-losing enteropathy.
protein-fibrinogen ratio
see plasma protein:fibrinogen ratio.
fibrous p's
characterized by shape, structure and low water solubility; they have a structural role. Examples are collagen, keratin and tropomyosin.
fusion protein
in recombinant DNA technology when a foreign gene is inserted into a plasmid vector to interrupt a gene, such as lacZ, the mRNA transcript of the recombinant plasmid contains the lacZ Shine-Dalgarno sequence and codons for the 3′ end of the lacZ gene protein followed by the codons of the foreign gene; the protein expressed is a fusion protein containing a few N-terminal lacZ amino acids and the contiguous foreign protein.
protein hydrolysates
pharmaceutical preparations used in the treatment of severe, acute protein loss. Available for use orally or parenterally. They are partly digested proteins and contain a mixture of polypeptides, amino acids and other breakdown products.
protein microarray
an ordered set of small samples of proteins immobilized on a microscope slide or other solid surface that is used to determine protein-protein interactions.
myeloma protein
see multiple myeloma.
protein nutritional deficiency
causes lack of muscle development, and slow growth rate and maturation. In adults there is a low milk production and poor weight gain. In severe states tissue and blood levels fall, hypoproteinemic edema may occur, and a degree of immunosuppression could be expected.
partial protein
one having a ratio of essential amino acids different from that of the average body protein.
peripheral protein
any protein located in the membrane but not essential to the reconstitution of that protein.
plasma p's
all the proteins present in the blood plasma, including the immunoglobulins. See plasma protein.
polyhedrin matrix protein
a protein that comprises the major component of occlusion bodies produced by nuclear polyhedrosis virus and cytoplasmic polyhedrosis virus; the strong polyhedrin promoter is utilized in the expression of recombinant proteins in baculovirus expression systems.
rec A protein
an enzyme that binds to DNA and plays an important role in genetic recombination.
protein S
a circulating vitamin K-dependent protein with anticoagulant effects.
serum protein
proteins in the blood serum, including immunoglobulins, albumin, complement, coagulation factors and enzymes.
protein shock
anaphylaxis occurring after the intravenous injection of protein.
in times of energy deficiency the animal body may raid protein stores for glucogenic amino acids, thus depleting body stores of proteins. Substances such as acetic acid which can fill the energy deficiency and avoid the protein loss are known as protein-sparing.
protein supplements
feeds which contain more than 20% protein.
urine protein
viral protein
proteins encoded by the viral genome.

Patient discussion about protein

Q. I get about 190 grams of protein a day. Is that too much protein? Have you ever seen a guy living only for food? No? Here I am. I get about 190 grams of protein a day. Is that too much protein? My weight is 183 pounds.

A. this is a good amount, just make sure that you get the majority of it from real foods and not from powders and bars.

Q. Does the cooking have a negative effect on the protein content of the food? I have heard that high temperatures cooking breaks the protein, so does the cooking have a negative effect on the protein content of the food?

A. Yes. Proteins can be denatured by heat, but only when the protein structure is delicate or is exposed to extremely high temperatures for long time. You must remember that breaking of protein is the physical-chemical process where the physical or chemical structure of a protein is rearranged. So cooking will not reduce on the nutritive value of the food until it’s cooked at cooking temperatures.

Q. Is it true that Casein protein can cause Cancer, or is harmful to the human body? Someone left a comment on my blog about Casein protein being bad for the body and that it could lead to Cancer. Is this true?

A. I am not familiar with such information, Casein is a protein that is found in large amounts in breastmilk and milk products replacements for babies and as far as I know it has no such affect.

More discussions about protein
References in periodicals archive ?
Sometimes, the insect protein is even better, he says.
The idea can be great, but the result for adoption will depend on many factors that are not always directly related to, for instance, a new technology for extracting insect proteins.
The insect protein encoded by Indy resembles several proteins in mammals that enable intestinal and kidney cells to take in metabolites, such as citrate, to produce energy.
This is why they entrap small insects in the globules formed at the end of the hairs -- which contain formic and benzoic acid that make up the digestive pepsin enzymes which break down the easily assimilated insect proteins.
Insect proteins such as cricket flour and ground mealworms are emerging ingredients.
The various classes of insect proteins include transport proteins, such as lipophorins in the hemolymph; regulatory proteins, including hormones of insects; defense proteins; and structural proteins, a variety of which are found in the cuticle (Neville 1975; Chapman 1998; Lenhninger et al.
The next step will be to use PIR technology to discover how the virion and the structural proteins interact with plant and insect proteins.
The quality of insect proteins is usually good too, compensating, Bukkens says, for what is lacking in largely vegetarian diets.