Change in Location of Ornithine Carbamoyltransferase and Carbamoylphosphate Synthetase among Yeasts in Relation to the Arginase/Ornithine Carbamoyltransferase Regulatory Complex and the Energy Status of the Cells

Abstract

Partial fractionation of Saccharomyces cerevisiae spheroplast lysate shows that arginase, ornithine carbamoyltransferase and carbamoylphosphate synthetase have the same distribution as the cytosol marker enzyme glucose‐6‐phosphate dehydrogenase. The same holds true in stepwise homo‐genization experiments of spheroplast lysates of S. cerevisiae . This second method applied to Debaryomyces hansenii, Hansenula anomala and Schizosaccharomyces pombe shows, in contrast, that ornithine carbamoyltransferase is particulate in these yeasts. Its solubilization is in line with that of citrate synthase taken as mitochondrial matrix marker, whereas arginase acts like glucose‐6‐phosphate dehydrogenase. In Schizosaccharomyces pombe carbamoylphosphate synthetase is particulate too. Density gradient centrifugation of a particulate fraction of Schizosaccharomyces pombe suggests that ornithine carbamoyltransferase and carbamoylphosphate synthetase are associated with the mitochondria. In Saccharomyces cerevisiae and in some other yeasts [Messenguy & Wiame (1969) FEBS Lett. 3 , 47–49; Wiame (1974) Proc. 9th Meet. Fed. Eur. Biochem. Soc. , pp. 161–177] arginase binds to ornithine carbamoyltransferase in the presence of arginine and ornithine, thereby inhibiting its activity but leaving arginase activity unmodified. This regulation by reversible stoechiometric interaction between the two enzymes prevents recycling of ornithine to arginine when the latter is used as a source of nitrogen. Results presented here show a correlation between the shift of ornithine carbamoyltransferase and carbamoylphosphate synthetase from mitochondrial to extramitochondrial fraction and the existence of arginase/ornithine carbamoyltransferase regulatory interaction. This regulation and extramitochondrial ornithine carbamoyltransferase are absent from obligate aerobe yeasts and may reflect an adaptation to the fermentative type of energy production.