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J Bacteriol. 1967 October; 94(4): 1052-1059
Copyright © 1967 American Society for Microbiology. All Rights Reserved.

Evidence for the Calvin Cycle and Hexose Monophosphate Pathway in Thiobacillus ferrooxidans¹

^a Department of Bacteriology, Brigham Young University, Provo, Utah 84601

ABSTRACT

The enzymes of the Calvin reductive pentose phosphate cycle and the hexose monophosphate pathway have been demonstrated in cell-free extracts of Thiobacillus ferrooxidans. This, together with analyses of the products of CO₂ fixation in cell-free systems, suggests that these pathways are operative in whole cells of this microorganism. Nevertheless, the amount of CO₂ fixed in these cell-free systems was limited by the type and amount of compound added as substrate. The inability of cell extracts to regenerate pentose phosphates and to perpetuate the cyclic fixation of CO₂ is partially attributable to low activity of triose phosphate dehydrogenase under the experimental conditions found to be optimal for the enzymes involved in the utilization of ribose-5-phosphate or ribulose-1,5-diphosphate as substrate for CO₂ incorporation. With the exception of ribulose-1,5-diphosphate, all substrates required the addition of adenosine triphosphate (ATP) or adenosine diphosphate (ADP) for CO₂ fixation. Under optimal conditions, with ribose-5-phosphate serving as substrate, each micromole of ATP added resulted in the fixation of 1.5 µmoles of CO₂, whereas each micromole of ADP resulted in 0.5 µmole of CO₂ fixed. These values reflect the activity of adenylate kinase in the extract preparations. The K_m for ATP in the phosphoribulokinase reaction was 0.91 x 10^–3M. Kinetic studies conducted with carboxydismutase showed K_m values of 1.15 x 10^–4M and 5 x 10^–2M for ribulose-1,5-diphosphate and bicarbonate, respectively.

² Present address: Bio-Sciences Division of Physical Research Center, TRW Systems, Redondo Beach, Calif.

¹ This work was taken from a dissertation by Nord L. Gale in partial fulfillment of the requirements for the Ph.D. degree.