Glutamate decarboxylase from barley embryos and roots. General properties and the occurrence of three enzymic forms.
Glutamate decarboxylase in extracts of barley has a Km value for L-glutamate of 22 mM and is activated by the addition of pyridoxal phosphate by up to 3.5 times. Sucrose-density-gradient experiments indicate the presence of two enzyme forms with molecular weights 256000 and 120000. The lower-molecular-weight form appears to be relatively inactive and spontaneously associates to the higher-molecular-weight form on storage. The enzyme is inhibited by thiol reagents and the distribution of activity on density gradients is altered in favour of the lower-molecular-weight form by the presence of 2-mercaptoethanol. After removal of the 2-mercaptoethanol spontaneous association to the higher-molecular-weight form occurs. The presence of oxygen in the extraction buffer and in the water during imbibition leads to a relative increase in the higher-molecular-weight form compared with situations where oxygen is excluded. In contrast, glutamate decarboxylase in extracts of 3-day-old barley roots has a Km value for L-glutamate of 3.1 mM and is activated up to 10% by addition of pyridoxal phosphate. The root enzyme occurs as a single species with molecular weight 310000 and this is unaffected by 2-mercaptoethanol although thiol reagents do act as weak inhibitors. The molecular weight is also unaffected by the presence or absence of oxygen in the extraction buffers.
D000429:Alcohol Oxidoreductases / Q000032:analysis; D002262:Carboxy-Lyases / Q000302:isolation & purification*; D002374:Catalase / Q000032:analysis; D003545:Cysteine; D004229:Dithiothreitol; D002523:Edible Grain / Q000201:enzymology*; D005968:Glutamate Decarboxylase / Q000032:analysis / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D001467:Hordeum / Q000201:enzymology*; D007527:Isoenzymes / Q000302:isolation & purification*; D007700:Kinetics; D008623:Mercaptoethanol; D008970:Molecular Weight; D010100:Oxygen
D007527:Isoenzymes; D008623:Mercaptoethanol; D000429:Alcohol Oxidoreductases; D002374:Catalase; D002262:Carboxy-Lyases; D005968:Glutamate Decarboxylase; D003545:Cysteine; D010100:Oxygen; D004229:Dithiothreitol