S-Adenosylhomocysteine hydrolase from rat liver

Abstract

The kinetic constants for the reversible adenosylhomocysteine hydrolase from rat liver were determined. The Km values of the enzyme for S-adenosylhomocysteine, adenosine and L-homocysteine were 12.3, 0.94, and 164 .mu.M, respectively. Under the specified conditions the Vmax for the synthetic reaction was 6.2 .mu.mol/min per mg, while the Vmax for the hydrolytic reaction was 0.72 .mu.mol/min per mg. L-Homocysteine acted as a mixed-type inhibitor of the hydrolytic reaction. Adenine, a competitive inhibitor of both the synthetic and hydrolytic reactions (Ki = 1.2 .+-. 0.2 .mu.M), was a product of the reaction. In the absence of L-homocysteine .apprx. 0.8 nmol of adenosine was hydrolyzed to adenine and ribose per min per mg enzyme.