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Biomedical subjects

D R Morris

Publications and source records attributed to D R Morris.

At least 109 records · Page 6Linked to original sources
PubMed1973

Growth and macromolecular composition of a mutant of Escherichia coli during polyamine limitation.

A mutant of Escherichia coli with reduced levels of biosynthetic arginine decarboxylase was isolated which required putrescine or spermidine for optimal growth. The stimulation of growth by putrescine was 1.5- to 3-fold depending upon the culture medium. Specificity studies supported the concept that the requirement was for spermidine or closely related polyamines, or for diamines which could be converted enzymatically to these compounds. The behavior of the macromolecular composition of the polyamine-starved cells appeared abnormal. The ribonucleic acid to protein and deoxyribonucleic acid to cell ratios in the starved cells were both higher than expected on the basis of their growth rate. The stable ribonucleic acid in the polyamine-limited cells appeared to be normal as judged from size distribution and degree of methylation. The relationship of these results to mechanisms for regulation of nucleic acid and protein synthesis in E. coli is discussed.

Arginine↗
PubMed1973

Influence of polyamine limitation on the chain growth rates of beta-galactosidase and of its messenger ribonucleic acid.

The rates of elongation of beta-galactosidase and its messenger ribonucleic acid (RNA) were estimated in a polyamine-deficient mutant of Escherichia coli through an analysis of the kinetics of enzyme induction. The chain growth of beta-galactosidase was calculated from the time required after the appearance of an amino terminal fragment of 60 amino acids (auto-alpha) until completed enzyme began to accumulate. The elongation rate of beta-galactosidase messenger RNA was estimated from the time after induction at which streptolydigen-resistant, enzyme-forming capacity first appeared. Upon polyamine starvation, the rate of polypeptide elongation slowed from 17 to 10 amino acids per s and the messenger RNA elongation rate decreased from 47 to 30 nucleotides per s. These reductions in polymerization rates were proportional to the decrease in cellular growth rate produced by polyamine starvation. It was concluded that, although it is quite unlikely that polyamine levels are involved in regulation of cell growth, they may be acting as cofactors in the synthesis of RNA or protein, or both.

Drug Stability↗
PubMed1970

Isolation of conditionally putrescine-deficient mutants of Escherichia coli.

Mutants defective in the conversion of arginine to putrescine were found by screening clones from mutagenized cultures for inability to produce urea during growth in arginine-supplemented media. Two partially blocked mutants were isolated; one was deficient in arginine decarboxylase and the other was deficient in agmatine ureohydrolase. As predicted from the pattern of putrescine synthesis in Escherichia coli, these mutants were conditionally putrescine-deficient. When grown in either minimal or ornithine-supplemented media, conditions which lead to preferential utilization of the ornithine to putrescine pathway, the mutants had normal intracellular polyamine levels. However, when the mutants were placed in arginine-supplemented media, the level of intracellular putrescine was lowered markedly. Under conditions where intracellular putrescine was 1% of normal, the doubling time of the mutants was increased approximately 10%. The putrescine-deficient mutants had wild-type morphology, normal levels of protein and ribonucleic acid (RNA), and stringent amino acid control of RNA synthesis.

Amines↗
PubMed1967

Urea production and putrescine biosynthesis by Escherichia coli.

Cultures of Escherichia coli B and K-12 produce urea during growth in minimal medium. Results of isotopic labeling experiments were consistent with the sole source of urea being from the conversion of arginine to putrescine. Since E. coli itself has no demonstrable urease activity, the rate of urea production is a measure of the flux through the arginine to putrescine pathway.

Amines↗