The purification and characterization of a minor legumin species from Pisum sativum is described. Electrophoretic data indicate that it corresponds to a legumin subunit pair previously designated L1. The beta-polypeptides of the minor legumin have a phenylalanine N-terminus. This is the first time that an amino acid other than glycine has been reported as the N-terminus of the basic polypeptides from legumin-like proteins from any plant species. Sequence analyses of the isolated alpha- and beta-polypeptides of the minor legumin show that it does not correspond to any of the three legumin gene families that have previously been defined on the basis of DNA hybridizations and genetic analyses.
A comparative study has been made of the ability of three plant tissues to incorporate 14 C into ethylene from 14 C-labelled methionine and derivatives and from 14 C-labelled linolenic acid. Incorporation of label occurs readily from methionine and its derivative 4-methylmercapto-2-oxobutyric acid with apple, tomato or cauliflower floret tissue. No incorporation of label occurred, however, from uniformly 14 C-labelled linolenate.
The enzyme responsible for the conversion of methionine into a precursor of ethylene in cauliflower florets is a transaminase. The formation of 4-methyl-mercapto-2-oxobutyric acid by this enzyme has been shown. The oxo acid stimulates the synthesis of ethylene when added to floret tissue, and tracer experiments have shown that 14 C is incorporated into ethylene from the labelled oxo acid. The evidence is consistent with the view that the oxo acid is an intermediate in the formation of ethylene from methionine.