A Comparison of Catalytic Properties of Glutamate Dehydrogenase from Liver and Muscle between Amphibious Periophthalmus cantonensis and Water-breathing Godbid Fishes Tridentiger

Abstract

The catalytic properties of glutamate dehydrogenase of the liver and muscle from an amphibious gobid fish, Periophthalmus cantonensis were conpared with those of the enzymes from a water-breating gobid fish, Tridentiger obscurus obscurus.
The enzyme activities in the liver and muscle of P. cantonensis increased to a greater degree with rising ambient salinities than those observed with T. obscurus obscurus, when they were acclimated in different salinities for 7 days.
The apparent Km for NH⁺₄ of the muscle enzyme from P. cantonensis was about half as much as that of the enzyme from T. obscurus obscurus, while those values of the liver enzymes from both species were essentially similar. No species-difference was observed in other kinetic constants of the enzymes from the two gobid fishes including the Km's for α-ketoglutarate and NADH, the Ka's for ADP and leucine and the Ki's for GTP (in the absence fo ADP), NAD⁺ and glutamate.
The effect of ADP on the liver enzyme from P. cantonensis was stronger than that of the enzyme from T. obscurus obscurus, while the effects of ADP on the muscle enzymes from both the species were similar. The effects of ADP on GTP-inhibited enzymes from P. cantonensis were much greater than the corresponding effects on the enzymes from T. obscurus obscurus. These results suggest that the enzymes from P. cantonensis were more tightly regulated by ADP-GTP interaction than the enzymes from T. obscurus obscurus.