| Abstract: | The differential synthesis of intracytoplasmic and whole cell phospholipids has been monitored in synchronously and asynchronously dividing cultures of Rhodopseudomonas sphaeroides by employing a non-specific deuterium labeling technique. Following the phototrophic growth of cells of R. sphaeroides in D₂O-based medium, mass spectrometric analysis of purified methyl esters of cis-vaccenate (the predominant (90%) fatty acid possessed by R. sphaeroides) revealed an average level of deuteration of 23 atoms of deuterium incorporated per fatty acid molecule. This level of acyl group deuteration was calculated to contribute over 70% of the increased specific density of membranes obtained from cells grown in deuterated medium. The deuterated and protonated species of methyl vaccenate were found to be separable by gas-chromatography, and by monitoring the decrease in the relative quantity of deuterated vaccentate to normally protonated vaccenic acid during a D₂O to H₂O growth transition, the production of cellular fatty acids could be monitored. This latter technique was employed to examine the pattern of membrane phospholipid production in cells of R. sphaeroides. |
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