[15-Hydroxyprostaglandin dehydrogenase from human placenta, II. Steady state kinetics and influence of prostaglandin F2alpha analogues (author's transl)].

A complete initial rate analysis of the forward reaction catalyzed by 15-hydroxyprostaglandin dehydrogenase from human term placenta was carried out at pH 7.4 (100mM triethanolamine) with the substrates NAD, and the prostaglandins E1, E2 and F2alpha. The limiting Michaelis constants, the dissociation constants, and the limiting maximum velocities for these substrates were calculated by fitting the obtained data by weighted linear regression analysis to the complete rate equation. The product inhibition of the reaction by NADH and 15-oxoprostaglandin was studied and the inhibition constants were graphically determined. The initial rate and inhibition patterns obtained indicate that the reaction follows kinetically an ordered Bi Bi mechanism. The prostaglandin F2alpha analogues ICI 81,008 and ICI 79,939 were not utilized by the enzyme. With ICI 81,008 a slight inhibition of the enzymatic reaction with prostaglandin F2alpha was observed, whereas ICI 79,939 showed no effect. The results are discussed with respect to their possible biological significance.