phosphorylase(redirected from Phosphorylase a)
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an enzyme that, in the presence of inorganic phosphate, catalyzes the conversion of glycogen into glucose-1-phosphate.
An enzyme cleaving poly(1,4-α-d-glucosyl)n with orthophosphate to form poly(1,4-α-d-glucosyl)n-1 and α-d-glucose 1-phosphate. The active form of the enzyme is a phosphorylated protein.
1. any of a group of enzymes that catalyze the phosphorolysis of glycosides, transferring the cleaved glycosyl group to inorganic phosphate. When not qualified with the substrate name, the term usually denotes glycogen phosphorylase (animals) or starch phosphorylase (plants).
2. any of a group of enzymes that catalyze the transfer of a phosphate group to an organic acceptor.
Any of a class of enzymes that catalyze the attachment of a phosphate group to another molecule.
Etymology: Gk, phosphoros, bringer of light + ase, enzyme suffix
any of a group of physiologically important enzymes that catalyze reactions between phosphates and glycogen or other starch components, yielding glucose-1-phosphate.
A phosphorylated enzyme cleaving poly(1,4-α-d-glucosyl)n with inorganic phosphate to form poly(1,4-α- d-glucosyl)n-1 and α-d-glucose 1-phosphate.
muscle enzymesthe table lists some of the most often-mentioned enzymes present in skeletal muscle, with their locations and functions. Apart from actomyosin and myosin ATPases which are associated with the contractile mechanism, they are by no means specific to muscle, being present and highly active also in other tissues. See also Krebs cycle, muscle fibre types.
|Actomyosin ATPase (amATPase) myosin head groups||hydrolysis (Mg-dependent and triggered by rise in [Ca2+]) of terminal phosphate group of ATP when head-group is in interaction with actin, releasing energy that powers force- generation. (Compare myosin ATPase)|
|Creatine kinase (CK) cytoplasm||transfer of phosphate group from creatine phosphate to ADP, producing ATP and creatine. Isoenzymes can be distinguished in blood when either skeletal or cardiac muscle has been damaged.|
|Hexokinase (HK) cytoplasm||'capture' of glucose after uptake from the blood, by conversion to the impermeant glucose 6-phosphate, in type 1 muscle fibres, which utilize glucose directly.|
|Lactate dehydrogenase (LDH) cytoplasm||reduction of pyruvate to lactate when oxygen tension is low, and the converse when it is high. Isoenzymes can be distinguished in blood when either skeletal or cardiac muscle has been damaged.|
|Myosin ATPase (mATPase) myosin head groups||hydrolysis (Ca2+ dependent, Mg2+ independent) of terminal phosphate group of ATP by head group alone, not interacting with actin (so not contraction-producing: cf actomyosin ATPase). Basic histochemical marker for fast vs. slow fibres.|
|Phosphofructokinase (PFK) cytoplasm||conversion of fructose 6-phosphate to fructose 1,6-diphosphate; rate-limiting for glycolysis, and sensitive to very many stimulatory and inhibitory influences.|
|Phosphorylase (PPL) cytoplasm||removal of hexose units, one at a time, from glycogen, to form glucose 1-phosphate: rate-limiting enzyme of, and histochemical marker for, glycogenolysis.|
|Pyruvate dehydrogenase (PDH) mitochondrial envelope||oxidative decarboxylation of pyruvate (from cytoplasm) to form acetyl CoA, which thence feeds into tricarboxylic acid (Krebs) cycle|
|Sarcoplasmic reticulum ATPase (srATPase) SR membrane||pumping of [Ca2+] back into SR after its electrically stimulated release|
|Succinate dehydrogenase (SDH) mitochondrial inner membrane||oxidation of succinate to fumarate, in tricarboxylic acid (Krebs) cycle. Histochemical marker for aerobic capacity.|
glycogenolysisremoval of a glucose molecule from glycogen, by the action of the enzyme glycogen phosphorylase, present in liver, kidneys, muscle and brain. The products are a glycogen molecule that is one glucose residue shorter than before and glucose-1-phosphate. This in turn is converted to glucose-6-phosphate, from which free glucose can be released from the liver and kidneys (but not from skeletal muscle or brain) by the action of glucose-6-phosphatase. See also glucose, glycolysis.
a key regulatory enzyme that, in the presence of inorganic phosphate, catalyzes the removal of one glucose unit from glycogen to glucose-1-phosphate.
see ornithine carbamoyl transferase.
an enzyme that activates phosphorylase by catalyzing the phosphorylation of serine. See also kinase.