Search PubMed⌕ Search

Biomedical subjects

J M Phang

Publications and source records attributed to J M Phang.

101 records · Page 6Linked to original sources
PubMed1970

Interaction between histidyl transfer ribonucleic acid and the first enzyme for histidine biosynthesis of Salmonella typhimurium.

Previous studies showed that the enzyme (phosphoribosyltransferase) which catalyzes the first step of the histidine pathway in Salmonella typhimurium plays a role in regulation of the histidine operon. Since histidyl transfer ribonucleic acid (His-tRNA) is required for repression of the histidine operon, we considered the possibility that the role of phosphoribosyltransferase might be realized through an interaction with His-tRNA. One prediction inherent in this idea is that the enzyme should interact with His-tRNA in vitro. Evidence is presented for such an interaction. Binding of (3)H-His-tRNA to purified phosphoribosyltransferase was tested on Sephadex columns and on nitrocellulose filters. The enzyme was found to have a high affinity for tRNA. Comparing the binding of (3)H-His-tRNA with that of tRNA aminoacylated with other (3)H-amino acids disclosed that the binding of the histidyl species of tRNA is favored over that of other species and is dependent upon magnesium-ion concentration.

Acrylates↗
PubMed1969

Studies on repression of the histidine operon. II. The role of the first enzyme in control of the histidine system.

Recent studies on repression of the enzymes for histidine bio-synthesis in Salmonella typhimurium demonstrated that the kinetic pattern in which the enzymes become repressed is influenced by the state of the feedback-sensitive site of the first enzyme of the pathway (Kovach et al., J. Bacteriol., 97, 1283 (1969)). In the present study we demonstrate that under certain conditions alteration of the feedback-sensitive site of the first enzyme prevents repression of the histidine operon. We conclude that the first enzyme plays a previously unrecognized role in regulation of the histidine system.

Binding Sites↗
PubMed1969

Dietary perturbation of calcium metabolism in normal man: compartmental analysis.

The effect of dietary calcium intake on calcium metabolism was studied in eight normal volunteers by multicompartmental analysis of radiocalcium and balance data. In paired studies of six normal subjects on normal and high or low calcium intakes, necessary and sufficient criteria were used to determine changes in calcium metabolic parameters produced by alterations in dietary calcium. These changes involved gastrointestinal calcium absorption rate, renal and endogenous fecal rate constants, and bone resorption rate. Bone accretion rate and compartment sizes need not change between the paired studies. The changes of parameters involving kidney, gut, and bone were in a direction to support calcium homeostasis and were compatible with the pattern of changes produced by parathyroid hormone. However, the source of the stimulus for hormone secretion was not apparent since plasma calcium concentrations showed no significant difference between paired studies. The implications of these findings relative to control of hormone secretion, calcium regulatory mechanisms, and metabolic bone disease are discussed.

Bone Resorption↗
PubMedDate not supplied

Proline biosynthesis and degradation in mammalian cells and tissue.

Radioisotopic assays have been developed for the enzymes of proline metabolism. These assays are specific and sensitive enough to measure enzyme activities in cultured cells and biopsy specimens. Measurements of these enzymes in tissues and cultured cells suggest that endogenous biosynthesis of proline may be an important source of this amino acid.

Animals↗