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Cell-free extracts and whole cell suspensions of Desulfovibrio vulgaris were employed to examine the fixation of 14CO2 into acid stable material. Moderate levels of CO2 fixation occured in the presence of ribulose-1,5-diphosphate, ribose-5-phosphate or pyruvate with only minimal levels of CO2 fixation occuring with formate, malate, or succinate. The fixation of CO2 in the presence of pyruvate was attributed to the pyruvate-CO2 exchange reaction. This exchange reaction was dependent on the presence of an acidic protein fraction but was not stimulated by the additions of ATP to the reaction mixture. The fixation of CO2 which was associated with ribose-5-phosphate or ribulose-1,5-diphosphate did require ATP for optimal activity and could be resolved from the pyruvate-CO2 exchange reaction since the pentose phosphate CO2 fixation did not require the acidic protein fraction. Maximal fixation of co 2 with pentose phosphates occured when the reaction wasincubated at 37 degrees c., at pH 8.0, and in the presence of magnesium ions.

The amount of CO2 fixed with ribose-5-phosphate was dependent on ATP concentration, enzyme concentration, and incubation time of the reaction. Phosphate, sulfate, sulfite, and thiosulfate at 0.32m greatly inhibited the fixation of CO2 with ribose-5-phosphate. An autoradiograph study of the products of the reaction revealed that with ribose-5-phosphate or ribulose-1,5-diphosphate the fixation of CO2 appeared to proceed by way of the reductive pentose cycle; however, with pyruvate in the reaction there was no evidence of radioactivity in the sugar phosphate.



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Department Name

UNM Biology Department

First Committee Member (Chair)

Larry L. Braton

Second Committee Member

Gordon Verle Johnson

Third Committee Member

Oswald H. Baca

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