Characterization of the binding of S-adenosyl-L-methionine to plasma membranes of HL-60 promyelocytic leukemia cells.

Abstract S- Adenosyl- l -methionine (AdoMet) has been found to bind specifically to the plasma membrane of promyelocytic leukemia cells. HL-60. The K d for AdoMet is 4.2·10 −6 M and the B max is 4.0·10 −12 mol/10 7 HL-60 cells. The binding is not related to the adenosine receptor since neither adenosine, ADP, nor ATP affect the ligand-receptor reaction. When HL-60 cells were incubated with physiological concentrations of [ methyl - 3 H]AdoMet (20 μM) at 36°C, AdoMet did not equilibrate with the intracellular pool, nor were any [ 3 H]methyl groups incorporated into nucleic acids or proteins. In contrast, significant amounts of [ 3 H]methyl groups were incorporated into membrane phospholipids. When cells were incubated with 20 μM [ methyl - 3 H]AdoMet, [ 3 H]methyl groups were transferred to phosphatidyl-ethanolamine, -monomethylethanolamine, and -dimethylethanolamine yielding phosphatidylcholine. However, the rate of methyl transfer with AdoMet was only 22% of that observed when cells were incubated with a comparable amount of [ methyl - 3 H]methionine. Both the binding of AdoMet and the methylation of phospholipids were inhibited by exogenous S- adenosyl- l -homocysteine . Therefore, the binding may be linked to a phospholipid methyltransferase.