(2)H- and(13)C-labeled amino acids generated by obligate methylotrophs Biosynthesis and MS monitoring

Biosynthetic preparation of(2)H- and(13)C- labeled amino acids was studied using a leucine-producing mutant of the obligate methylotroph,Methylobacillus flagellatum. The strain was cultivated in various media containing(13)C- or(2)H-analogs of methanol. The total protein from each experiment was subjected to acid hydrolysis and converted into a mixture of dansyl amino acid methyl esters. The samples of excreted leucine were converted into methyl esters of dansyl and benzyloxycarbonyl derivatives. Electron impact mass spectrometry was performed to detect stable isotope enrichment of the amino acids. According to the mass spectrometric analysis it is feasible to use methylotrophic microorganisms for the preparation of(2)H- and(13)C- analogs of amino acids by labeled methanol bioconversion; the excreted amino acids can be convenient for express analysis as an indicator of isotopic enrichment of the total protein. The data obtained testified to a high efficiency of dansyl derivatization for mass spectrometric analysis of complex amino acid mixtures.