Reductive Pentose Phosphate Cycle in Nitrosocystis oceanus

Abstract
Assays in cell-free extracts of N. ocenaus, a marine chemoautotrophic bacterium, have demonstrated The presence of all of the enzymes of the reductive pentose phosphate cycle, with activities high enough to account for the normal growth rate of the cells. Studies on ribulosediphosphate carboxylase activity in these extracts showed that it is inhibited by MgCl2 (30% at 0.01 [image]), MnCl2 (70% at 0.01 [image]), NaCl and KC1 (100% at 0.5 [image], 63% at 0.2 [image]), and by sulfate (35% at 0.01 [image]); phosphate, glutathione, and ethylene-diaminetetraacetic acid had no effect. The bacterial enzyme differs from the spinach enzyme with respect to its affinity for bicarbonate and its pH optimum. Whole cells were incubated with C14 O2, and the acid-soluble fraction was analyzed by paper chromatography and autoradiography. Phosphoglyceric acid and the sugar phosphates were the earliest labeled compounds; several amino-acids and organic acids were also labeled. It is concluded that N. oceanus incorporates CO2 primarily via the reductive pentose phosphate cycle.