Glycogenphosphorylase
Glycogen phosphorylase ( PYG) (more precisely: 1,4- α -D-glucan: phosphate - α -D - glucosyl transferase ) is a cytosolic enzyme of glycogen metabolism, which catalyzes the phosphorolytic cleavage of glycogen to glucose -1-phosphate. It comes in the sub-forms PYGB before (brain, heart), PYGM (muscle ) and PYGL ( liver).
Background
The sugar is glucose, a central molecule in the energy metabolism and biosynthetic precursor of a large number of biologically important compounds, including non-essential amino acids, fatty acids, inter alia, glycogen is a polymer of glucose units, and is for the animal organism as a storage form of glucose similar to the starch in plants. Mobilization of glucose from glycogen storage molecule to the catalytic activity of glycogen phosphorylase is required.
Structure and Properties
The glycogen phosphorylase is a homodimer with a monomer mass of 97 kDa ( human). There are three isoforms of the brain (BB), muscle (MM) and liver (LL) glycogen phosphorylase. All isoenzymes require pyridoxal phosphate for activity. The KM values for glycogen located in the upper uM to lower mM range. Glycogen phosphorylase is inhibited by glucose and ATP, and activated by AMP, wherein the expression of the Effektorwirkung depending on the isoform. The specific activity is in the range of several tens of U / mg protein.
Genetic disorders
Genetic defects of Muskelisoform of glycogen phosphorylase lead to McArdle 's disease. Mutations in the liver isoform can lead to Crohn's Hers. For the brain isoform no such disease is known.
Glycogen phosphorylase BB
The Glykogenphophorylase BB ( GPBB ), is one of the isoforms of glycogen phosphorylase and is used in medical diagnostics.
The glycogen phosphorylase BB is found in the heart muscle and in the brain in high concentration. When ischemia is caused by activation of the GPBB an increased glycogen breakdown. The liberated GPBB passes quickly into the bloodstream. This GPBB comes as biomarkers ( specifically than before " heart attack markers " ) in the laboratory diagnostics in heart attack in question.