Edwin C. Webb

On the homology of the active-site peptides of liver carboxylesterases

Abstract 1. 1.Highly purified preparations of liver carboxylesterases (carboxylic ester hydrolases, EC 3.1.1.1) from pig, sheep, ox and chicken were stoichiometrically labelled with [32P]DFP, and then subjected to peptic digestion. 2. 2.Radioactive peptides were isolated from the peptic digests by chromatography on Sephadex G-25, paper chromatography and high voltage electrophoresis. For each species, an octapeptide was isolated as the major radioactive peptide. 3. 3.Amino acid analyses of pig and sheep octapeptides were identical with the previously published analysis of the corresponding octapeptide from horse liver carboxylesterase. Analyses of ox and chicken octapeptides both indicated single amino acid substitutions when compared with the horse octapeptide. 4. 4.The two amino acid substitutions were located by conventional sequencing procedures. In the ox octapeptide, alanine replaces the glycine three residues from the labelled serine towards the C-terminal. In the chicken peptide, isoleucine replaces the glutamic acid residue four removed from the serine towards the C-terminal. The possible significance of the amino acid substitutions is discussed in terms of other properties of the enzymes.

3,4-dihydroxybenzaldehyde, a fungistatic substance from green Cavendish bananas

A fungistatic substance has been isolated from the outer skin of green Cavendish bananas and identified as 3,4-dihydroxybenzaldehyde. The compound has been shown to inhibit the growth of Gloeosporium musarum, a fungus which causes ripe fruit rot in the banana.

Primary structure of cytochrome c from the elephant seal, Mirounga leonina☆

Twenty-seven peptides, including the haemopeptide, were isolated from a single chymotryptic digest of seal heart cytochrome c by chromatography on Sephadex G-75, Whatman phosphocellulose P-70 and Bio-Rad AG 50W-X2. These peptides were purified by electrophoresis or chromatography on paper and their sequences were determined. The complete sequence of the protein was deduced by alignment of these peptides by comparison with the known sequences of several other cytochromes c. Seal cytochrome c differs from the dog and horse proteins in 1 and 6 positions, respectively. The single difference from dog cytochrome c is found in position 100 where isoleucine, in the seal, replaces the lysine found in the dog.