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Biomedical subjects

G Lowe

Publications and source records attributed to G Lowe.

173 records · Page 10Linked to original sources
PubMed1968

The location of the active-site histidine residue in the primary sequence of papain.

Papain that had been irreversibly inhibited with 1,3-dibromo[2-(14)C]acetone was reduced with sodium borohydride and carboxymethylated with iodoacetic acid. After digestion with trypsin and alpha-chymotrypsin the radioactive peptides were purified chromatographically. Their amino acid composition indicated that cysteine-25 and histidine-106 were cross-linked. Since cysteine-25 is known to be the active-site cysteine residue, histidine-106 must be the active-site histidine residue.

Acetone↗
PubMed1968

Evidence for histidine in the active sites of ficin and stem-bromelain.

1. Ficin and stem-bromelain are irreversibly inhibited by 1,3-dibromoacetone, a reagent designed to react first with the active-site cysteine residue and subsequently with a second nucleophile. Evidence is presented that establishes that a histidine residue is within a 5A locus of the active-site cysteine residue in both enzymes. The histidine residue in both enzymes is alkylated at N-1 by dibromoacetone. It is suggested that, as with papain, the thiol and imidazole groups act in concert in the hydrolysis of substrates by these enzymes. 2. The inhibition of thiol-subtilisin with 1,3-dibromoacetone is shown to be due to the alkylation of a cysteine residue only.

Acetone↗
PubMed1967

Lysozyme-catalysed hydrolysis of some beta-aryl di-N-acetylchitobiosides.

1. Four beta-aryl di-N-acetylchitobiosides and beta-S-phenyl di-N-acetylthiochitobioside have been prepared and shown to be substrates for hen's-egg-white lysozyme. 2. The lysozyme-catalysed hydrolysis of these substrates obeys Michaelis-Menten kinetics. 3. The Michaelis constants, K(m), for the beta-aryl di-N-acetyl-chitobiosides are almost independent of the aglycone, whereas the catalytic constants, k(cat.), show a marked dependence, giving a Hammett reaction constant, rho, equal to 1.2; this suggests the rate-determining step involves concerted acid-base or acid-nucleophilic catalysis. 4. This conclusion is supported by the Michaelis-Menten constants found for beta-S-phenyl di-N-acetylthiochitobioside. 5. A three-step reaction pathway is proposed, and mechanisms are suggested that would account for the evidence currently available.

Animals↗
PubMed1966

The kinetics of papain- and ficin-catalysed hydrolyses in the presence of alcohols.

1. The maximum rate of production of p-nitrophenol (V(max.)) for both papain- and ficin-catalysed hydrolyses of p-nitrophenyl hippurate is independent of methanol concentration up to 2m for papain and 1.5m for ficin. 2. The observed catalytic constant (k(0)) for the production of hippuric acid for both papain- and ficin-catalysed hydrolyses of methyl hippurate decreases with increasing methanol concentration, 1/k(0) being linearly dependent on the methanol concentration. The k(MeOH)/k(H2O) ratio is determined. 3. These results provide strong evidence against general base catalysis for the rate-determining step in the deacylation of hippuryl-papain and hippuryl-ficin and probably for other specific acyl-papains and acyl-ficins. 4. The rate-determining step for the deacylation of the non-specific trans-cinnamoyl-papain appears to be different from that for the specific hippuryl-papain, and is probably subject to general base catalysis. It is possible, however, to accommodate all these observations in a single four-step reaction pathway. 5. Propan-2-ol did not influence the rate of production of hippuric acid for the papain-catalysed hydrolysis of methyl hippurate. A similar result has previously been reported for the ficin-catalysed hydrolysis of methyl hippurate. Ethanol and of course methanol (see 2) decrease the rate of production of hippuric acid for both papain- and ficin-catalysed hydrolyses of methyl hippurate. It is suggested that the secondary alcohol is incapable for structural reasons of approaching the bond to be hydrolysed.

1-Propanol↗