Role of Phosphatidylethanolaminb N-Methylation on Ca²⁺ Transport in Cardiac Membranes

Abstract

Evidence is accumulating that lipid composition of the membrane plays an important role in a variety of membrane-mediated functions of the myocardial cell, including the activities of membrane-bound enzymes and ion transport systems (1–6).The intramembranal rearrangement of the two major membrane phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC), can occur through three successive N-terminal methylations of PE where S-adenosyl-L-methionine (AdoMet) is the physiological methyl donor (7). In previous studies we have described the characteristics of three methyltransferase catalytic sites (I, II and III) for PE N-methylation in cardiac subcellular membranes which can be readily identified at 0.055 - 0.1, 10 and 150 μM concentrations of AdoMet (8). Under optimal conditions, predominant synthesis of specific phospholipid molecules, namely phosphatidyl-N-monomethylethanolamine (PMME), phosphatidyl-N, N-dimethylethanolamine (PDME) and PC was found to occur in heart membranes at sites I, II and III, respectively. The methyltransfer scheme is illustrated in Figure 1.Since the physical state of the cell membrane is determined by several chemical modulators including the methylation of PE polar head group (9). it is plausible that PE N-methylation may participate in regulating different membrane functions.