Metabolism of bis(monoacylglycero)phosphate in macrophages.

To further elucidate the role of bis(monoacylglycero)phosphate in lysosomes, its metabolism was assessed by incubation of intact and disrupted macrophages in the presence of labeled lipid precursors. In rabbit pulmonary macrophages bis(monoacylglycero)P accounted for 17.9% and acylphosphatidylglycerol for 2.6% of phospholipid phosphorus. Major fatty acids in bis(monoacylglycero)P were oleic (47%), linoleic (29%), and arachidonic (6.4%); those in acylphosphatidylglycerol were of similar distribution except for a high content of palmitic acid (20%). When homogenates of rabbit pulmonary and peritoneal macrophages, rat pulmonary macrophages, and human blood leukocytes were incubated with sn[(14)C]glycerol-3-phosphate and CDP-diacylglycerol at pH 7.4, there was labeling of bis(monoacylglycero)P and acylphosphatidylglycerol that correlated with content of bis(monoacylglycero)P. When intact rabbit pulmonary macrophages were incubated for 60 min with [(3)H]glucose and [(32)P]orthophosphate, small amounts of label appeared in bis(monoacylglycero)P and only traces in acylphosphatidylglycerol. In contrast, incubation of intact cells with the (14)C-labeled fatty acid precursors palmitic, oleic, and arachidonic acids resulted in much greater labeling of the two lipids. Labeling of phospholipids was greatest with arachidonate as precursor and least with palmitate; after 60 min, labeling of bis(monoacylglycero)P with arachidonate was 10- and 50-fold greater than with oleate and palmitate, respectively, and was exceeded only by that of phosphatidylcholine. Calculated ratios of labeling of fatty acid to P, particularly those for arachidonate, were much greater for bis(monoacylglycero)P and for acylphosphatidylglycerol than for other phospholipids. This suggests a uniquely high turnover of fatty acids in bis(monoacylglycero)P and acylphosphatidylglycerol and thus a more specific role for these compounds in metabolism of complex lipids in the lysosome.-Huterer, S., and J. Wherrett. Metabolism of bis(monoacylglycero)phosphate in macrophages.