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Biomedical subjects

G B Irvine

Publications and source records attributed to G B Irvine.

68 records · Page 4Linked to original sources
PubMed1986

High-performance gel permeation chromatography of proteins and peptides on columns of TSK-G2000-SW and TSK-G3000-SW: a volatile solvent giving separation based on charge and size of polypeptides.

Trifluoroacetic acid (0.1% w/v) is an excellent solvent for polypeptides, is volatile, and has a low absorbance of ultraviolet light of low wavelength. Polypeptides subjected to chromatography on columns of TSK-G2000-SW or TSK-G3000-SW in this solvent were eluted as sharp peaks. Retention volume was dependent not only on molecular weight but also on the number of formal charges per molecule. For polypeptides with a similar molecular weight, that with the highest proportion of basic amino acid residues was eluted earliest. For the TSK-G2000-SW column, the degree of deviation from a linear relationship between elution volume and logarithm of molecular weight was directly proportional to the molecular weight to the power 2/3 divided by the number of positive charges per molecule. Inclusion of 0.25 M sodium chloride in the solvent increased both the upper and lower limits of the molecular weight range over which separation occurred. The use of 0.1% trifluoroacetic acid as the mobile phase is thus particularly applicable to the separation of peptides of low molecular weight.

Chromatography, Gel↗
PubMed1983

The kinetics of hydrolysis of some synthetic substrates containing neutral hydrophilic groups by pig pepsin and chicken liver cathepsin D.

1. Several peptides containing either of the sequences -Phe(NO2)-Trp- and -Phe(NO2)-Phe- and an uncharged hydrophilic group were synthesized, and the steady-state kinetics of their hydrolysis by pig pepsin (EC 3.4.23.1) and chicken liver cathepsin D (EC 3.4.23.5) were determined. Despite the presence of a hydrophilic group to increase substrate solubility, it was not possible to achieve the condition [S]0 much greater than Km, and, in some cases, only values of kcat./Km could be determined by measuring the first-order rate constant when [S]0 much less than Km. 2. Occupancy of the P2 and P3 sites considerably enhanced the specificity constant, and alanine was more effective than glycine at site P2. 3. The specificity constants for the hydrolysis by pepsin of those substrates in the present series that contain an amino acid residue at site P3 are considerably lower than for comparable substrates containing a cationic group. This difference does not apply to cathepsin D. 4. Hydrolyses with cathepsin D commonly exhibited a lag phase, and a possible explanation for this is given.

Animals↗
PubMed1979

A radiochemical titrant for the determination of the operational molarity of solutions of acid proteinases.

N-Diazoacetyl-L-phenylalanine 3-phenyl[2,3-3H]propylamide was synthesized and shown to inhibit pepsin A (EC3,4,23.1) and cathepsin D (EC 3.4.23.5) irreversibly and stoicheiometrically in the presence of Cu2+. Quantitative separation of the inhibited enzyme from excess reagent by gel filtration followed by measurement of the radioactivity of the protein peak provided a method for determining the operational molarity of these enzymes. Several other putative active-site-directed irreversible inhibitors were synthesized, but were inactive. Data on the synthesis of these compounds have been deposited as Supplementary Publication SUP50096 (4 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.

Azo Compounds↗
PubMedDate not supplied

Dioxygen and the vitamin K-dependent synthesis of prothrombin.

It has been shown that bovine erythrocyte superoxide dismutase inhibits the gamma-carboxylation of glutamyl residues in the precursor of prothrombin and in a related synthetic peptide by a vitamin K-dependent rat liver microsomal carboxylase. In the same conditions a simple copper(II) tyrosinyl complex also inhibits the carobxylation. The formation of the vitamin K epoxide by the same systems is inhibited by both superoxide dismutase and catalase. It is suggested that the formation of the epoxide is a process distinct from carboxylation, representing perhaps a protective mechanism against the superoxide ion, or species derived therefrom, generated by the reaction of reduced vitamin K with dioxygen. Furthermore, the possibility that the carboxylating species is formed by the reaction of the superoxide ion, or species derived therefrom, with carbon dioxide, is proposed.

Animals↗
PubMedDate not supplied

Effects of some neurokinin A analogues on tachykinin-induced contraction of guinea pig trachea.

A series of analogues of neurokinin A (NKA) has been synthesized and characterized by testing for their abilities, in vitro, to contract guinea pig tracheal smooth muscle or to antagonize NKA-, NKB- and SP-induced contraction of this tissue. Substitution of NKA residues Gly8 or Leu9 by conformationally restricting amino acids produced peptides that were antagonists of NKA action, but the type and specificity of the antagonism depended on the size of the peptide. Thus, while [Ala5, Aib8, Leu10]NKA(2-10) showed no agonism and was a specific, competitive antagonist of NKA, [Ala5, Aib8, Leu10]NKA(4-10) was a noncompetitive antagonist of NKA and substance P (SP) and was itself a weak agonist at concentrations above 10(-7) M.

Amino Acid Sequence↗