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Biomedical subjects

A S Whitworth

Publications and source records attributed to A S Whitworth.

4 recordsLinked to original sources
PubMed1982

A comparison of free T4 and the ratio of total T4 to T4-binding globulin in serum through pregnancy.

Serum free T4 concentrations have been variously reported as either constant or falling in pregnancy. In this study, 122 serum samples from apparently normal pregnancies were used to derive euthyroid ranges throughout pregnancy for T4 and free T4 (measured by the Amerlex kits) and for T4-binding globulin (TBG). The mean free T4 concentration fell with increasing gestational age, the range of values in the third trimester being narrower than the non-pregnant normal range. Evidence is reviewed which shows that the Amerlex free T4 assay is unaffected by the elevation of TBG in non-pregnant subjects. The decline in mean free T4 as pregnancy proceeds is in good agreement with the change in free T4 predicted by the falling T4/TBG ratio.

Alpha-Globulins↗
PubMed1974

A kinetic and fluorimetric investigation of papain modified at tryptophan-69 and -177 by N-bromosuccinimide.

A systematic study of the modification of papain (its thiol group protected as a disulphide with mercaptoethanol) by N-bromosuccinimide, showed that 2 molar equiv. modified tryptophan-69 and 4 molar equiv. modified tryptophan-69 and -177. The Michaelis parameters for the catalysed hydrolysis of N-benzyloxycarbonylglycine p-nitrophenyl ester by these modified enzymes were determined. The enzymic activity of the modified enzymes was not seriously impaired, but modification of tryptophan-177 raised the apparent pK(a) of the acidic limb of the pH profile by more than 1 pH unit for both k(cat.) and k(cat.)/K(m). The fluorescence spectra (excitation at 288nm) of the modified enzymes showed that tryptophan-69 contributed about 8% to the fluorescence intensity, whereas tryptophan-177 contributed about 46% at neutral pH. However, the contribution of tryptophan-177 was quenched at low pH and its fluorescence intensity showed sigmoidal pH-dependence, with an apparent pK(a) of 4.2. Histidine-159, which is in close contact with tryptophan-177, is considered to be the residue responsible for the fluorescence quenching. When tryptophan-177 was modified, presumably generating a less hydrophobic micro-environment, the apparent pK(a) determined kinetically was raised to about 5.4. By comparing the Michaelis parameters of native papain, papain modified at tryptophan-69 and papain modified at tryptophan-69 and -177 with N-benzyloxycarbonylglycylglycine amide and N-benzyloxycarbonylglycyltryptophan amide, tryptophan-69 and tryptophan-177 were shown to be structural features of the S(2) and S(1)' subsites respectively.

Amino Acid Sequence↗