Some enzymes and properties of the reductive carboxylic acid cycle are present in the green alga Chlamydomonas reinhardtii F-60

Abstract

The reductive carboxylic acid cycle, the autotrophic pathway of CO2 assimilation in prokaryotes (photosynthetic and nonphotosynthetic autotrophic bacteria), was investigated in Chlamydomonas relnhardtli F-60, an algal mutant lacking a complete photosynthetic carbon reduction pathway (C3) due to a deficiency in phosphoribulokinase. Evidence was obtained consistent with the presence of the reductive carboxylic acid cycle in F-60. This conclusion is based on the fact that: (a) acetate approximately doubled CO2 fixation in whole cells (4 micromoles per milligram chlorophyll per hour) and in chloroplasts (32 nanomoles per milligram chlorophyll per hour); and (b) pyruvate synthase, α-ketoglutarate synthase, and ATP-citrate lyase, three indicators of the cycle, were found in cell-free extracts.