AMP-deaminase from human uterine smooth muscle: the effect of DTNB treatment on kinetic and regulatory properties of the enzyme.

Reactivity of sulfhydryl groups of human uterine smooth muscle AMP-deaminase with DTNB, and the effect of their chemical modification on kinetic and regulatory properties of the enzyme were investigated. (1), Approx. 7 and 5 sulfhydryl groups per mol of the enzyme have been shown to be accessible for DTNB (5,5'-dithiobis(2-nitrobenzoic acid)) titration in denaturated and native AMP-deaminase, respectively. (2), Titrated groups were not homogenous; some of them reacted with DTNB much faster than others. (3), The activity of the modified enzyme was very low, and the modified enzyme manifested unusual hyperbolic saturation kinetics with the substrate. (4), Exhaustive dialysis against a buffer containing 10 mM thioethanol reactivated the modified enzyme, and restored its original regulatory properties. Experimental results obtained indicate that modified sulfhydryl groups play a significant role in the maintenance of the proper, catalytically-efficient conformation of the enzyme.