Discovery of sphingosine 1-O-methyltransferase in rat kidney and liver homogenates.

To characterize sphingosine methyltransferase in rat tissues. By using S-adenosyl-L-(methyl-3H) methionine, enzymatic activity was measured in the rat liver and kidney homogenates. The optimum pH and reaction time for the enzyme assay were pH 7.8 and 1 h. ZnCl2 inhibited the activity, but not MgCl2, CaCl2, CoCl2, or NiCl2. In the kidney homogenate, enzymatic activity was detectable in the cytosol and all membrane fractions from the plasma membrane and other organelles; however, in the liver homogenate, enzymatic activity was detectable in all membrane fractions, but not in the cytosol. We also tested the enzymatic activity with structurally-modified sphingosine derivatives. We found sphingosine 1-O-methyltransferase activity in the rat liver and kidney homogenates.