Enzymatic properties of glyceraldehyde-3-phosphate dehydrogenase from fish muscle

1. Glyceraldehyde-3-phosphate dehydrogenase was isolated from the ordinary muscle of red sea bream Pagrus major, Pacific mackerel Scomber japonicus and carp Cyprinus carpio by ammonium sulfate fractionation, followed by DEAE-Sepharose CL-6B and DEAE-cellulose column chromatography and Sephadex G-150 gel filtration, and examined for enzymatic properties. 2. Their optimum pH values in the backward reaction ranged from 7.8 to 8.2, and Km values from 1.56 to 1.90 mM. 3. Irrespective of the species of fish, the enzymatic activity was non-competitively inhibited by inorganic phosphate in the backward reaction. Divalent metal ions were not necessary to activate these glyceraldehyde-3-phosphate dehydrogenases. In the presence of 1 mM Zn(2+), these enzymes showed relative activities of 42-64% the activities measured in the absence of those ions. 5. Thermal stability of carp enzyme was higher than those of red sea bream and Pacific mackerel; the enzyme activity of the latter two species was almost lost on incubation at 45 degrees C for 10-20 min, whereas carp enzyme retained half the activity even when incubated at 60 degrees C for 30 min.