Unusual C3 and C4 metabolism in the chemoautotroph Alcaligenes eutrophus.

AUTOR(ES)

Schobert, P

RESUMO

Phosphoenolpyruvate (PEP) carboxykinase was identified to be the only C3-carboxylating enzyme in Alcaligenes eutrophus. The enzyme requires GDP or inosine diphosphate (GTP or inosine triphosphate) for activity. Pyruvate- and other PEP-dependent CO2-fixing enzyme activities were not detected, regardless of whether the cells were grown autotrophically or heterotrophically. It is suggested that two pathways are present in the organism for the formation of PEP from C4 dicarboxylic acids. Besides decarboxylation of oxaloacetate by PEP carboxykinase, the consecutive action of NADP+-malic enzyme and PEP synthetase can also accomplish this synthesis. An oxaloacetate decarboxylase activity observed in the cell extracts may also contribute to the latter route. The properties of a mutant deficient in PEP synthetase supported the biochemical data. This mutant was unable to grow on pyruvate or lactate and grew slower than the wild type on direct or indirect metabolites of the tricarboxylic acid cycle such as succinate, glutamate, or acetate. Growth on fructose and autotrophic growth were not affected by the enzyme defect. The findings suggest that, depending on the growth substrate utilized, PEP carboxykinase can serve a dual physiological function in A. eutrophus, an anaplerotic function in oxaloacetate synthesis from PEP, or a gluconeogenic function in PEP synthesis from oxaloacetate.

Documentos Relacionados

• The Calvin cycle enzyme pentose-5-phosphate 3-epimerase is encoded within the cfx operons of the chemoautotroph Alcaligenes eutrophus.
• Oxygen Requirement and Inhibition of C4 Photosynthesis1 : An Analysis of C4 Plants Deficient in the C3 and C4 Cycles
• Efficiency of Nitrogen Utilization in C3 and C4 Cereals.
• Regulation of early complement components C3 and C4 in the synovium.
• Differential expression of complement C3 and C4 in the human kidney.