Dissertation - Open Access
Doctor of Philosophy (PhD)
Carl A. Westby
Purine-thiamine anabolism during cellular morphogenesis in Myxococcus xanthus was investigated. One of the approaches was to test vegetative and myxospore (2.5 h and 8 h) extracts of M. xanthus CW-2 for their ability to synthesize the second de novo intermediate, 5'-phosphoribosylglycinamide, from beginning precursors either by way of phosphoribosyl-pyrophosphate amidotransferase (EC 18.104.22.168) or ribose-5-phosphate aminotransferase. Results indicate the presence of both the amido- and aminotransferases in both types of extracts, and both enzymes appear to be present at about the same level (per milligram of protein) in vegetative cells, myxospores (2.5 h and 8 h), and in a bacterial prototype, Salmonella typhimurium. The dose response of the CW-2 vegetative and myxospore amido- and aminotransferases towards AMP and GMP suggests that the allosteric structure of both enzymes is changed little by sporulation. Both the CW-2 amido- and aminotransferases were inhibited to varying degrees by a variety of purine nucleotides besides AMP, GMP, and 3':5' cyclic AMP. The second approach in determining whether purine-thiamine anabolism functions in M. xanthus during cellular morphogenesis was to use whole cells. Whole cells (vegetative, myxospore and germinating cells) were used to measure glycine, adenine, and guanine uptake and to test for the intracellular conversion of glycine-2-14C to 14C ATP and GTP. A thin-layer chromatographic-radioautographic method was employed to detect 14C ATP and GTP. The finding that purine de novo partially repressed cells (vegetative, myxospore and germinating CW-1) take up glycine faster than fully repressed cells suggests that the purine de novo pathway can function throughout the life cycle of M. xanthus. The rate of glycine uptake is reduced about 50% during the first hour of glycerol-induced myxospore formation and germinating myxospores take up glycine, adenine, and guanine more rapidly than the other cell types. Purine uptake studies suggest the presence of interconversion and salvage routes in M. xanthus. The thin-layer chromatographic-radioautographic studies indicate that glycine-2-14C is converted to 14C ATP and GTP. A thiamine-like substance was also detected by this method and it may be related to myxospore induction. No evidence was found to support the presence of highly phosphorylated compounds or the magic spot during the life cycle of this organism. A model for the thiamine or succinyl-CoA control of myxospore formation in M. xanthus is presented. This model proposes that a thiamine substance or succinyl-CoA may be a catabolite repressor or corepressor of myxospore (and fruiting-body) formation.
Library of Congress Subject Headings
Purines -- Metabolism
Vitamin B1 -- Metabolism
South Dakota State University
Tsai, Wen-Cherng, "Purine-Thiamine Anabolism During Cellular Morphogenesis in Myxococcus Xanthus" (1976). Electronic Theses and Dissertations. 5544.