A rapidly metabolizing pool of phosphatidylglycerol as a precursor of phosphatidylethanolamine and diglyceride in Bacillus megaterium

Abstract

Pulse-chase experiments in Bacillus megaterium ATCC 14581 with [U-14C]palnitate, L-[U-_4C]serine, and [U-'4C]glycerol showed that a large pool of phosphatidylglycerol (PG) which exhibited rapid turnover in the phosphate moiety (PGJ) underwent very rapid interconversion with the large diglyceride (DG) pool. Kinetics of DG labeling indicated that the fatty acyl and diacylated glycerol moieties of PGt were also utilized as precursors for net DG formation. The [U-'4C]glycerol pulse-chase results also confirmed the presence of a second, metabolically stable pool of PG (PG.), which was deduced from [32P]phosphate studies. The other major phospholipid, phosphatidylethanolamine (PE), exhibited pronounced lags relative to PG and DG in "C-fatty acid, [14C]glycerol, and [P]phosphate incorporation, but not for incorporation of L-[U-'4C]serine into the ethanolamine group of PE or into the serine moiety of the small phosphatidylserine (PS) pool. Furthermore, initial rates of L-[U-'4C]serine incorporation into the serine and ethanolamine moieties of PS and PE were unaffected by cerulenin. The results provided compelling in vivo evidence that de novo PGt, PS, and PE syntheses in this organism proceed for the most part sequentially in the order PGt-+ PS-+ PE rather than via branching pathways from a common intermediate and that the phosphatidyl moiety in PS and PE is derived largely from the corresponding moiety in PGt, whereas the DG pool indirectly provides an additional source for this conversion by way of the facile PGt ± DG interconversion.

Characterization of a membrane-associated cytidine diphosphate-diacylglycerol-dependent phosphatidylserine synthase in bacilli

“…On the other hand, the data of Lombardi et al (17) suggests that such a pathway for phosphatidylserine synthesis may not be necessary in the strain of B. megaterium which they investigated. Langley et al (14) reported results similar to those of Lombardi et al (17), but concluded that their results were due to a large, slowly metabolized pool of phosphatidylserine.…”

“…On the other hand, the data of Lombardi et al (17) suggests that such a pathway for phosphatidylserine synthesis may not be necessary in the strain of B. megaterium which they investigated. Langley et al (14) reported results similar to those of Lombardi et al (17), but concluded that their results were due to a large, slowly metabolized pool of phosphatidylserine. We were able to detect a membrane-associated phosphatidylserine synthase activity in B. megaterium (ATCC 14581), as were Langley et al (14), with similar properties to the B. licheniformis activity, but due to its low level we were unable to characterize it fully (data not shown).…”

“…Silber et al (28), working with another gram-positive anaerobe, Clostridium butyricum, noted the formation of radiolabeled phosphatidylserine from phosphatidic acid labeled in the acyl chains in a coupled in vitro assay of CDPdiacylglycerol synthase and phosphatidylserine synthase; this observation supports the existence of a CDP-diacylglycerol-dependent phosphatidylserine synthase in this organism. In addition, this activity was shown to be membrane associated as judged by sucrose gradient centrifugation, thus establishing a membrane location for this activity in a gram-positive anaerobe. There has been a recent report describing in vivo pulse-chase experiments on B. megaterium (ATCC 14581) which indicate a precursor-product relationship between a rapidly metabolizing pool of phosphatidylglycerol and phosphatidylserine, respectively, suggesting no requirement for a CDP-diacylglycerol-dependent phosphatidylserine synthase activity in this organism (17).…”

Biosynthesis of D-alanyl-lipoteichoic acid: role of diglyceride kinase in the synthesis of phosphatidylglycerol for chain elongation

“…In a number of bacteria, PG is present in two distinct pools (1,2,17,18) with different rates of metabolic turnover. In B. megaterium, one pool of PG undergoes rapid turnover whereas the other exhibits metabolic stability.…”

“…In B. megaterium, one pool of PG undergoes rapid turnover whereas the other exhibits metabolic stability. It has been suggested that the former pool is the donor of GroP units for LTA synthesis (17,18). Recently, Brautigan et al suggested that toluene-treated cells of L. casei synthesize a unique population of PG in the presence of excess phosphate (4).…”