Enzyme(redirected from brancher enzyme, branching enzyme)
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Enzymes work by binding molecules so that they are held in a particular geometric configuration that allows the reaction to occur. Enzymes are very specific; few molecules closely fit the binding site. Each enzyme catalyzes a specific type of chemical reaction between a few closely related compounds, which are called substrates of the enzyme.
Enzymes are given names ending in -ase. In older names, the suffix is added to the name of the substrate, as in amylase, an enzyme that breaks down the polysaccharide amylose. In newer names, the suffix is added to the type of reaction, as in lactate dehydrogenase, an enzyme that converts lactate to pyruvate by transferring a hydrogen atom to nicotinamide-adenine dinucleotide (NAD).
In allosteric regulation, the enzyme can bind molecules, which are referred to as effectors, at a site other than the active site, which is referred to as an allosteric site. In many biochemical pathways the enzyme that catalyzes the first reaction in the pathway is inhibited by the final product of the last reaction, so that when sufficient product is present the whole pathway is shut down. This is an example of negative feedback.
Many enzymes are regulated by phosphorylation. A phosphate group is attached to the enzyme by another enzyme, called a protein kinase. When the enzyme is phosphorylated it changes its shape and thus its activity. Phosphorylation activates some enzymes and inactivates others; by this means one protein kinase can control several enzymes.
All enzymes are controlled by their rate of synthesis. Like all proteins, enzymes are synthesized by ribosomes, which translate the genetic information coded in the deoxyribonucleic acid (DNA) of the chromosomes into the specific amino acid sequence of the enzyme. The expression of many genes is controlled by the processes of genetic regulation. Thus, although each cell contains the information to make all of the body's enzymes, it actually makes only those appropriate for its specific type of cell. The synthesis of some enzymes can be induced or repressed by the action of specific hormones, substrates, or products so that the enzyme is produced only when metabolic conditions require its presence.
An example of an aminoacidopathy is phenylketonuria (PKU), which results from a deficiency of the enzyme phenylalanine hydroxylase, which converts the amino acid phenylalanine to tyrosine. Phenylalanine accumulates in the blood and phenylpyruvic acid is excreted in the urine. The phenylalaninemia eventually results in mental retardation due to defective formulation of myelin. However, PKU can be detected at birth by a screening test for phenylalanine in the blood, and clinical symptoms can be avoided by strict adherence to a low-phenylalanine diet.
An example of a lysosomal storage disease is tay-sachs disease, which results from a deficiency of the enzyme hexosaminidase A. The stored substance is a sphingolipid, GM2-ganglioside, which accumulates in nerve tissue, causing blindness and mental deterioration. No cure is possible, but antenatal diagnosis can be made by determining hexosaminidase A activity in fetal fibroblasts from an amniotic fluid specimen drawn by amniocentesis. It is also possible to identify carriers (heterozygotes) who are at risk for having children with the disease.
enzymeA protein that catalyzes most chemical reactions in biological systems without itself being destroyed or altered by the reaction; enzymes accelerate the rate of reactions by lowering transition state energy Enzyme Commission groups Oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase.
enzymeA biochemical catalyst that enormously accelerates a chemical reaction. Enzymes are complex protein molecules highly specific to particular reactions. Almost everything that happens in the body, at a chemical level, is mediated by one or more of the many thousands of different enzymes in the cells, and much of the length of each DNA molecule consists of codes for enzymes.
enzymea protein molecule that catalyses a biochemical reaction by lowering the ACTIVATION ENERGY required for the reaction to proceed. Enzymes are usually specific to particular substrates (see ACTIVE SITE) and are sensitive to environmental conditions such as pH and temperature (see Fig. 149, and Q10 ). ALLOSTERIC ENZYMES exist in inactive and active forms, while others can be inhibited by nonsubstrate molecules (see COMPETITIVE INHIBITION, NONCOMPETITIVE INHIBITION). Protein-splitting enzymes (PROTEASES) are produced in nonactive forms in the mammalian digestive system to minimize the risk of self-digestion. For example, TRYPSIN is produced as inactive trypsinogen.
Patient discussion about Enzyme
Q. My muscle enzymes are at 355, my DR says normal is 200. She refered me to a Neurologist. What could be wrong? I am experiencing sore legs when I walk, weakness, and sometimes difficulty in swallowing. I am 46 I had a minor heart attack 5 yrs ago with a stent placed in my LAD. I am on Crestor 10mg. my Dr. has adjusted the dosage several times and used other drugs but it doesn't change the results much if at all.