S-Adenosylhomocysteine hydrolase from rat liver

Abstract

The kinetic constants for the reversible adenosylhomocysteine hydrolase from rat liver have been determined. The Km values of the enzyme for S-adenosylhomocysteine, adenosine, and L-homocysteine were 12.3 μM, 0.94 μM, and 164 μM respectively. Under the specified conditions the Vmax for the synthetic reaction was 6.2 μmol/min per milligram, while the Vmax for the hydrolytic reaction was 0.72 μmol/min per milligram. 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 μM), was found to be a product of the reaction. In the absence of L-homocysteine about 0.8 nmol of adenosine was hydrolyzed to adenine and ribose per minute per milligram enzyme.