Dissociation of an enzyme complex from Neurospora crassa

Genetics and biochemistry of carbamoyl phosphate biosynthesis and its utilization in the pyrimidine biosynthetic pathway.

“…Williams and Davis (159) claimed that UTP stabilized CPSpyr at 0°C and had no effect at 25°C, whereas L-glutamine stabilized at 25°C but not at 0°C. In our hands, neither UTP nor L-glutamine had any significant effect on coldor warm-mediated inactivation (95).…”

“…The larger form could be converted to the smaller form in vitro, but not vice versa (28). In the light of recent observations in a number of organisms, it seems probable that the smaller ACT form is a product of proteolysis of the larger (95,124).…”

“…A lowmolecular-weight form at 100,000 was also found, also posessing ACT activity but lacking CPSpyr activity. This latter form was shown to be a fragment of the native complex arising by endopeptidase attack on the native form when purification had removed the endopeptidase inhibitor (95). This 100,000-dalton fragment differs from the native ACT in its affinity for L-aspartate, which is higher, and in its activation by glycine (92).…”

Proteolytically induced changes in the molecular form of the carbamyl phosphate synthetase-uracil-aspartate transcarbamylase complex coded for by the URA2 locus in Saccharomyces cerevisiae

“…A single polypeptide chain responsible for the three first enzymatic activities of the pyrimidine pathway was purified to homogeneity from hamster cells in culture (5). However, in S. cerevisiae (26), N. crassa (27,28), Drosophila melanogaster (16,32), Rana castebiena (19), and mammalian cells (14,33) the experimental data show that the apparent molecular form of the complex is heterogeneous. In some of these cases an independent form of ATCase was found consistently, which was dissociated from the CPSase-uracil.…”

Metabolism of Pyrimidines and Purines

“…The pyrimidine-specific CPS is associated with ATC in a multienzyme complex of 650,000 which is encoded from the pyrimidine-3 gene through a unique mRNA starting in the CPS part. Purification studies on the CPS-ATC complex were of limited success due to the presence of an endogenous protease (MAKoFF and RADFORD 1977) and the instability of CPS (WILLIAMS et al 1971). Using a genetic approach a complex of two A TC trimers were proposed by , linked by three CPS dimers which were composed in two domains of six homologous subunits.…”