Determination of S-adenosylmethionine and S-adenosylhomocysteine in nuclei isolated from sea urchin embryos during early development.

S-adenosylmethionine (SAM) is the most important methyl donor in a wide variety of biological methylation processes. The demethylated produce, S-adenosylhomocysteine (SAH), is an intermediate in the transfer of sulfur from methionine to cysteine and regulates methylation reactions by its strong inhibition of many methyltransferase enzymes. For many years in our laboratory we studied DNA and protein methylation in nuclei isolated from sea urchin embryos an incubated in vitro in presence of SAM, as methyl donor.