부산대학교 도서관

Studies of the reversible interconversion of glycine and serine catalyzed by rabbit liver serine transhydroxymethylase in the presence and in the absence of tetrahydrofolate are described. The studies include measurements of pH-rate profiles, isotope effects, and spectral properties of the enzyme-substrate complexes. Vmax, values for the synthesis of serine from glycine and formaldehyde and the exchange of the 2Sproton of glycine with protons of the solvent were found to be constant between pH 6.0 and 8.0. The Vmaxfor the degradation of serine to glycine and formaldehyde decreased as the pH was increased from 6.0 to 8.4. A dissociable group on the enzyme with a pK of about 7 appears to be involved. An isotope effect of 2 was found for [2S-2H]glycine in the synthesis of serine both in the presence and in the absence of tetrahydrofolate. The rate of serine synthesis in the presence of tetrahydrofolate is limited at high enzyme concentration by the rate of the nonenzymatic formation of 5,10-methylenetetrahydrofolate.