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Biomedical subjects

R H Davis

Publications and source records attributed to R H Davis.

At least 235 records · Page 13Linked to original sources
PubMed1973

Use of external, biosynthetic, and organellar arginine by Neurospora.

The fate of very low amounts of (14)C-arginine derived from the medium or from biosynthesis was studied in Neurospora cells grown in minimal medium. In both cases, the label enters the cytoplasm, where it is very briefly used with high efficiency for protein synthesis without mixing with the bulk of the large, endogenous pool of (12)C-arginine. The soluble (14)C-arginine which is not used for protein synthesis is sequestered in a vesicle with the bulk of the endogenous arginine pool. After this time, it is selectively excluded from use in protein synthesis except by exchange with cytoplasmic arginine. The data suggest that in vivo, the non-organellar cytoplasm contains less than 5% of the soluble, cellular arginine. The cellular organization of Neurospora described here also prevents the catabolism of arginine. Our results are discussed in relation to previous work on amino acid pools of other eukaryotic systems.

Arginine↗
PubMed1972

Carbamoyl phosphate compartmentation in Neurospora: histochemical localization of aspartate and ornithine transcarbamoylases.

Carbamoyl phosphate is required for arginine and pyrimidine synthesis. In the arginine pathway, it is used in the ornithine transcarbamoylase (EC 2.1.2.1) reaction; in the pyrimidine pathway, it is used in the aspartate transcarbamoylase (EC 2.1.3.2) reaction. In Neurospora crassa, two pathway-specific enzymes catalyze the synthesis of carbamoyl phosphate, and two path-specific pools of carbamoyl phosphate are maintained. Histochemical studies show that ornithine transcarbamoylase is located in mitochondria, and, with less certainty, that aspartate transcarbamoylase is confined largely to nuclei. The enzymes that form carbamoyl phosphate are associated with the respective transcarbamoylases in the cell. Therefore, the segregation of carbamoyl phosphate pools could be accounted for by one or both organellar membranes, which demarcate two separate sites of carbamoyl phosphate metabolism in Neurospora. The alternative possibility that the enzyme complex that produces and consumes carbamoyl phosphate in the pyrimidine pathway could explain the channelling of carbamoyl phosphate, wholly or in part, is discussed.

Aspartic Acid↗