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Biomedical subjects

M Hill

Publications and source records attributed to M Hill.

At least 415 records · Page 23Linked to original sources
PubMed1977

Surgical management of airway obstructions during sleep.

Anatomical or physiological airway obstructions during sleep, of which the patient is unaware, cause daytime sleepiness at first, then signs of decreasing mental function, and eventually in some individuals, pulmonary and systemic hypertension. A few of these patients had been recognized before, the Pickwickian syndrome and in children with cardiac problems and large tonsils. The majority, however, present as sleep disorders. This paper describes our surgical experience with improving the airways of 19 children and adults with daytime somnolence.

Adolescent↗
PubMed1976

The production of urinary phenols by gut bacteria and their possible role in the causation of large bowel cancer.

Epidemiological evidence is presented to relate the amount of dietary meat to the risk of large bowel cancer; it has been suggested that this may be due to the production of cocarcinogenic volatile phenols by intestinal bacteria from tyrosine. This paper describes preliminary experiments to test this suggestion. In vitro, aerobic bacteria tended to produce phenol from tyrosine while anaerobic bacteria produced p-cresol. Urine from 10 normal healthy persons contained a mean of 9.8 mg phenol/day and 51.8 mg p-cresol/day. Results from studies on patients with ileostomy, colostomy, and diverticular disease indicated that p-cresol is largely produced by the anaerobic flora of the left colon while phenol was produced in the ileum (when colonized) and cecum. In patients with familial polyposis the activity of the aerobic flora was apparently normal but there was greatly reduced amounts of p-cresol produced. The amounts of urinary volatile phenols in six patients with newly diagnosed large bowel cancer were not different from the normal values, indicating that cocarcinogenic phenols were unlikely to be a major cause of the disease.

Adult↗
PubMed1976

Endogenous DNA polymerase of a transformation-defective rous sarcoma virus: characterization and comparison with the enzyme of the non-defective parent.

An RNA-directed DNA polymerase associated with transformation-defective (td) segregant of Rous sarcoma virus (RSV) has been characterized. The enzyme required both a monovalent and a divalent cation, a sulfhydryl reducing agent, and all four deoxyribonucleoside triphosphates for the expression of maximal activity. Sensitivity of the endogenous RNA-directed DNA polymerase activity to a low concentration of pancreatic RNase indicated that the enzyme utilized the td virus endogenous RNA as template. Maximal DNA synthesis was observed in a reaction mixture of pH 8 - 8.5 at 45 C with a manganese concentration of 1 mM. The enzyme of the td virus responded to exogenous template-primers in a manner characteristic of DNA polymerase of RNA tumor viruses, and the response became substantially greater when noncomplementary precursors were omitted from the reaction mixture. The endogenous reaction kinetics were examined. Three phases of DNA synthesis could be distinguished. Evidence was obtained showing that during the third and slowest phase of DNA synthesis the reaction mixture was not depleted of precursors and that the enzyme was fully active to initiate DNA synthesis with newly-added viral or synthetic RNA templates. Comparison of TMP and dAMP incorporation kinetics suggested that at the initial phase the enzyme preferentially copies A-rich region(s) of viral RNA. A comparison was also made between the endogenous reaction of the td virus and that of its parent sarcoma virus. The pH optimum, metal ion requirements, effect of sulfhydryl agents, response to exogenous template-primers, and kinetics of DNA synthesis, were all compared. No significant difference between the reaction of the td virus and its sarcomatogenous counterpart could be demonstrated.

Avian Sarcoma Viruses↗
PubMed1975

Resonance Raman spectroscopic studies of the interactions between trypsin and a competitive inhibitor.

Raman spectroscopy was used to study the interactions between bovine trypsin and a competitive inhibitor. For this purpose, a chromophoric substrate analogue, 4-amidino-4'-dimethylamine azobenzene, was synthesized. This compound competitively inhibits the enzyme with a 1:1 stoichiometry and an inhibition constant Ki of 2.3 muM at pH 6.08 and 15 degrees. Resonance Raman spectra in aqueous solution of free or enzyme-bound inhibitor were analyzed. The main spectral changes observed upon enzyme-inhibitor complex formation were changes in the relative intensities of four bands (1171, 1206, 1315, 1608 cm-1) while no large frequency shifts occurred. The binding of the inhibitor molecule to the enzyme did not induce a twisting of the phenyl groups around the N=N bond. Some modifications of the band widths are interpreted in terms of a restriction of rotational motions in the inhibitor molecule. The possible involvement of specific interactions between trypsin and the benzamidinium ion part of the inhibitor molecule is discussed.

Azo Compounds↗