抄録
Kinetical analysis on the self-control mechanism of corticoid-induced F-GOTgave the following results.Corticoid-induced F-GOT might be one of K class allosteric enzymes and a typical ex-ample of oligomeric enzyme. This enzyme catalyzes the reaction of the forward directionin the presence of L-aspartate and a-ketoglutarate for the following three reasons:(a) F-GOT, particularly homotropic one showing positive cooperativity, shows asigmoid curve in relation to the initial steady-state velocity (Vi) to substrate concentra-tion ([S]), rather than a rectangular hyperbola to be expected from the Michaelis-Mentenrelationship. Apparently, the allosteric transition is also recognized in a cturve of doublereciprocal (Lineweaver-Burk) plot of Vi vs. [S], (b) F-GOT responds to a positive modula-tor with a change in apparent Km(:[84 ;), but without a change in maximum velocity(V=..). This fact proves it to be K enzyme, and (c) Desensitized allosteric F-GOT whichhas lost its previous sensitivity to modulators shows normal Michaelis-Menten kinetics.In this case, a change in V.... in response to the substrate without a change in Michaelisconstant (Km:[5]..), is recognized. This fact proves the catalytic site to be the V form.Such sites are similar to one another. The following consideraiton is put forth: Funda-mentally, F-GOT at a normal steady-state level may exist in a desensitized form ofallosteric F-GOT which has been released by corticoid treatment during the period ofsecondary adaptable responses.Although an excess in substrate resulted in an inhibition of the enzyme activity, thesigmoidal inhibitory curve showed that the kinetic characteristic was not necessarily thesame among enzymes, including an atypical one. It was considered that each enzymemight have been affected differently with its substrate by virtue of its own characteristics.
