Highly purified dihydrofolate reductase of calf thymus

Abstract

A procedure has been developed for the preparation of essentially pure dihydrofolate reductase (5,6,7,8-tetrahydrofolate: NAD(P)⁺ oxidoreductase, EC 1.5.1.3) from calf-thymus glands. The following criteria of purity were observed: The preparation exhibited only a single protein component by sedimentation ultracentrifugation, sedimentation equilibrium, sucrose gradient centrifugation, and Sephadex chromatography; with a mean mol. wt. of 33 500.

Electrophoresis on acrylamide gel showed only a single boundary. The pH-activity curve, relative substrate specificity, Michaelis constants of the substrates, and the SH character of the enzyme have been determined. Monovalent cations and Mg²⁺ enhanced the enzyme activity. Other divalent cations and sulfhydryl reagents were inhibitory. No stimulation of enzyme activity could be obtained by organic mercurials or urea.