The enzymatic synthesis of S-adenosyl-L-[2(n)-3H]homocysteine

The chemical synthesis of high specific-activity [35S]adenosylhomocysteine

The study of the family of transmethylases, critical to normal cellular function and often altered in cancer, can be facilitated by the availability of a high specific-activity S-adenosylhomocysteine. We report the two-step preparation of [35S]adenosylhomocysteine from [35S]methionine at a specific activity of 1420 Ci/mmol in an overall yield of 24% by a procedure involving demethylation of the [35S]methionine to [35S]homocysteine followed by condensation with 5'-chloro-5'-deoxyadenosine. The ease of the reactions, ready availability and low cost of the reagents and high specific-activity and stability of the product make the procedure an attractive one with many uses, and superior to current methodology.

An improved rapid assay for S-adenosyl-L-homocysteine hydrolase

A coupled enzyme system was devised to assay S-adenosyl-L-homocysteine hydrolase activity spectrophotometrically and to stain the hydrolase selectively in polyacrylamide gels. The assay procedure monitors the formation of uric acid derived from the catabolism of the adenosine moiety of S-adenosylhomocysteine. The staining procedure allows the determination of the molecular weight of the hydrolase when extracts are electrophoresed on polyacrylamide gradient gels and compared to standard of known molecular weight. The specificity of the enzyme for the homocysteine moiety was also investigated by testing modified compounds as substrates. All the analogs tested were inactive as substrates for hydrolysis, indicating a strict specificity.