A component of genetic variation among mice in activity of transmembrane methyltransferase I determined by the H-2 region.

The effects of the mouse major histocompatibility complex, H-2, on phospholipid methyltransferase I and II activities were investigated on hepatocyte membranes from inbred, congenic and recombinant strains. Each methyltransferase was assayed individually by measuring the incorporation of radiolabel from S-adenosyl-L-[methyl-3H]methionine into endogenous phospholipids. Our results indicate that H-2 exerted a significant effect on methyltransferase I but not on methyltransferase II activity. Thus, as in lower eukaryotes, two distinct enzymes were involved in methylation of phosphatidylethanolamine (PE) to phosphatidylcholine (PC). In addition, this effect was localized to the K end of the major histocompatibility complex by the use of recombinant haplotypes.