Characterization of S-propenyl- l-cysteine sulfoxide as the principal endogenous substrate of l-Cysteine sulfoxide lyase of onion

Abstract

The infrared and ultraviolet absorption spectra of the precursor to the lachrymator trans-(+)- S-propenyl- l-cysteine sulfoxide in onion are presented. This amino acid is converted to pyruvic acid by the l-cysteine sulfoxide lyase of a particulate fraction of onion and by the l-cysteine C-S lyase of Albizzia lophanta. The kinetic constants for this reaction and the fact that this substrate is the preponderant l-cysteine sulfoxide derivative in onion demonstrate that it is the principal endogenous substrate for the onion l-cysteine sulfoxide C-S lyase. Evidence is given for the presence in enzyme reaction mixtures of elemental sulfur previously postulated as a product of the enzyme reaction but not of propionaldehyde or 2-methyl-2-pentenal previously found in the vapor above such reaction mixtures. It is concluded that the reaction products comprise a complex mixture of substances derived from the primary sulfur-containing enzymatic product, 1-propenyl sulfenic acid.