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J Bacteriol. 1969 November; 100(2): 962-968
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Enzymes of Intermediary Carbohydrate Metabolism in the Obligate Autotrophs Thiobacillus thioparus and Thiobacillus neapolitanus¹

^a Bruce Lyon Memorial Research Laboratory, Children's Hospital Medical Center of Northern California, Oakland, California 94609

ABSTRACT

Levels of enzymes operative in the Embden-Meyerhof-Parnas (glycolytic) pathway, pentose phosphate cycle, citric acid cycle, and certain other phases of intermediary carbohydrate metabolism have been compared in Thiobacillus thioparus and T. neapolitanus. All enzymes of the glycolytic pathway except phosphofructokinase were demonstrated in both organisms. There were some striking quantitative differences between the two organisms with respect to the activities of the individual enzymes of the glycolytic pathway and the citric acid cycle. Qualitative differences were also found: the isocitrate dehydrogenase activity of T. thioparus is strictly nicotinamide adenine dinucleotide phosphate (NADP)-dependent, whereas that of T. neapolitanus is primarily nicotinamide adenine dinucleotide-dependent, activity with NADP being low; the glucose-6-phosphate dehydrogenase of T. thioparus is particulate, whereas that of T. neapolitanus is partly soluble and partly particulate; the 6-phosphogluconate dehydrogenase of T. thioparus is soluble, that of T. neapolitanus is partly soluble and partly particulate. All enzymes which function in the carbon reduction cycle were present at very high levels. In contrast, enzymes which operate exclusively in cycles other than the carbon reduction cycle were present at low levels. Of the enzymes not operative in the carbon reduction cycle that were examined, isocitric dehydrogenase had the highest specific activity. Both organisms possessed reduced nicotinamide adenine dinucleotide dehydrogenase activity. The qualitative and quantitative aspects of the data are discussed in relation to possible biochemical explanations of obligate autotrophy.

² Present address: Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, La. 70112.

¹ Presented in part at the 68th Annual Meeting of the American Society for Microbiology, Detroit, Mich., 5 May 1968.