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A Mitchell

Publications and source records attributed to A Mitchell.

At least 289 records · Page 16Linked to original sources
PubMed1979

Enzymes of pyrimidine metabolism in Mycoplasma mycoides subsp. mycoides.

The major pathways of ribonucleotide biosynthesis in Mycoplasma mycoides subsp. mycoides have been proposed from studies on its use of radioactive purines and pyrimidines. To interpret more fully the observed pattern of pyrimidine usage, cell extracts of this organism have been assayed for several enzymes associated with the salvage synthesis of pyrimidine nucleotides. M. mycoides possessed uracil phosphoribosyltransferase, uridine phosphorylase, uridine (cytidine) kinase, uridine 5'-monophosphate kinase, and cytidine 5'-triphosphate synthetase. No activity for phosphorolysis of cytidine was detected, and no in vitro conditions were found to give measurable deamination of cytidine. Of the two potential pathways for incorporation of uridine, our data suggest that this precursor would largely undergo initial phosphorolysis to uracil and ribose-1-phosphate. Conversely, cytidine is phosphorylated directly to cytidine 5'-monophosphate in its major utilization, although conversion of cytidine to uracil, uridine, and uridine nucleotide has been observed in vivo, at least when uracil is provided in the growth medium. Measurements of intracellular nucleotide contents and their changes on additions of pyrimidine precursors have allowed suggestions as to the operation of regulatory mechanisms on pyrimidine nucleotide biosynthesis in M. mycoides in vivo. With uracil alone or uracil plus uridine as precursors of pyrimidine ribonucleotides, the regulation of uracil phosphoribosyltransferase and cytidine 5'-triphosphate synthetase is probably most important in determining the rate of pyrimidine nucleotide synthesis. When cytidine supplements uracil in the growth medium, control of cytidine kinase activity would also be important in this regard.

Cell-Free System↗
PubMed1978

Body movement and inattention in learning-disabled and normal children.

Four experiments were conducted to test various aspects of an optimal level of arousal model of hyperactivity in learning-disabled children. Vigilance performance and level of body movement were measured while learning-disabled and control children performed in an auditory vigilance task. The results suggested that body movement increased throughout the vigilance task, increased rates of external stimulation result in decreased level of body movement, and learning-disabled children differed from controls in showing higher levels of body movement and poorer vigilance performance. The results were discussed in terms of changes in arousal level and compensatory stimulus-seeking behavior.

Arousal↗
PubMed1978

Enzymes of purine metabolism in Mycoplasma mycoides subsp. mycoides.

The major pathways of ribonucleotide biosynthesis in Mycoplasma mycoides subsp. mycoides were proposed previously from studies of its usage of radioactive purines and pyrimidines. To interpret more fully the pattern of purine usage, we have assayed cell-free extracts of this organism for several enzymes associated with the salvage synthesis of purine nucleotides. M. mycoides possessed phosphoribosyltransferases for adenine, guanine, and hypoxanthine, purine nucleoside phosphorylase, GMP reductase, GMP kinase, adenylosuccinate synthetase, and adenylosuccinate lyase. Purine nucleoside kinase and adenosine deaminase were not detected. Examination of kinetic properties and regulation of some of the above enzymes revealed differences between M. mycoides and Escherichia coli. Most notable of these were the greater susceptibility of the enzymes from M. mycoides to inhibition by nucleotides and the more widespread involvement of GMP as an inhibitor. Observations on enzyme activities in vitro allow an adequate explanation of the capacity of guanine to provide M. mycoides with its full requirement for purine nucleotides.

Adenosine Monophosphate↗
PubMed1978

The effect of supplemental vitamin E on vitamin A serum levels in cystic fibrosis.

Effects of the ingestion of vitamin E with vitamin A on the serum levels of these vitamins and the urinary creatine to creatinine ratios of 18 children with cystic fibrosis disease of the pancreas (CF) was studied. After the daily ingestion for two months of a specially prepared capsule containing 5000 IU vitamin A palmitate and 100 mg d alpha-tocopherol acetate in aqueous dispersible form there was a significant increase in vitamin A as well as vitamin E levels of serum taken 3 1/2 hr postprandially. Creatine to creatinine ratios in single voiding of urine decreased.

Adolescent↗
PubMed1977

Pathways of nucleotide biosynthesis in Mycoplasma mycoides subsp. mycoides.

By measuring the specific activity of nucleotides isolated from ribonucleic acid after the incorporation of (14)C-labeled precursors under various conditions of growth, we have defined the major pathways of ribonucleotide synthesis in Mycoplasma mycoides subsp. mycoides. M. mycoides did not possess pathways for the de novo synthesis of nucleotides but was capable of interconversion of nucleotides. Thus, uracil provided the requirement for both pyrimidine ribonucleotides. Thymine is also required, suggesting that the methylation step is unavailable. No use was made of cytosine. Uridine was rapidly degraded to uracil. Cytidine competed effectively with uracil to provide most of the cytidine nucleotide and also provided an appreciable proportion of uridine nucleotide. In keeping with these results, there was a slow deamination of cytidine to uridine with further degradation to uracil in cultures of M. mycoides. Guanine was capable of meeting the full requirement of the organism for purine nucleotide, presumably by conversion of guanosine 5'-monophosphate to adenosine 5'-monophosphate via the intermediate inosine 5'-monophosphate. When available with guanine, adenine effectively gave a complete provision of adenine nucleotide, whereas hypoxanthine gave a partial provision. Neither adenine nor hypoxanthine was able to act as a precursor for the synthesis of guanine nucleotide. Exogenous guanosine, inosine, and adenosine underwent rapid cleavage to the corresponding bases and so show a pattern of utilization similar to that of the latter.

Mycoplasma mycoides↗
PubMed1972

Malaria epidemic.

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Disease Outbreaks↗