Kinetics of rabbit muscle D-glyceraldehyde 3-phosphate dehydrogenase: inhibition by adenine nucleotides

Abstract

The inhibitory effects of adenine nu­ cleotides (ATP, ADP and AMP) on rab­ bit muscle D-glyceraldehyde 3-phosphate dehydrogenase (GPDH) have been investi­ gated. Concentrations for 50 % inhibition at2X10~4MNAD+and4.5X10-4M glyceraldehyde 3-phosphate (G3P) were determined as 1.5 X 10-3 M; 4.6 X 10-3 M and 6.8 X 10“3 M for ATP, ADP and AMP respectively. The degree of inhibi­tion, which is very small at pH 9, is ma­ ximal at approx. pH 7.5. The relationship between reaction velocity at pH 7.4 and NAD+ concentration is sigmoid (n = 2) but becomes hyperbolic (n = 1) in the presence of ATP. Increasing ATP concen­ trations decrease the VmaI. whilst having no effect on the Km for NAD (2.7 X 10~5 M), suggesting non-competitive inhibition with respect to NAD+. Plots of reaction velocity against increasing G3P concen­ trations are sigmoid (n = 1.7). ATP inhi­ bits GPDH with respect to G3P without altering the apparent order of reaction. In this case, VmaI. is unchanged and the S(0.5) for G3P is increased from 3.2 X 10-5 M to 5.4 X 10-5 M. The metabolic and enzymological significance of the data is discussed.