BEHAVIOR OF α-SUBSTITUTED CYSTINES IN A CYSTATHIONASE SYSTEM AND IN A PYRIDOXAL PHOSPHATE MODEL SYSTEM

Abstract

The behavior of several new α-substituted cystines synthesized in this laboratory (α-methyl-, α-ethyl-, α-n-propyl-, α -n-butyl-, α-isopropyl-, and α-phenyl-DL-cystine) was studied in a cystathionase system and in a pyridoxal phosphate model system.The substituted cystines were neither cleaved by cystathionase nor were they degraded in the model system consisting of pyridoxal phosphate with or without cupric ions. Under the latter conditions, L-cystine reacted even in the absence of added metal. Copper ions, however, increased the rate of degradation of the amino acid. The α-hydrogen atom was apparently required for reactivity.The enzymatic system with cystathionase, isolated from rat liver and purified to some extent, was inhibited competitively by L-cystine and the substituted sulfur amino acids. Inhibition by the natural substrate, L-cystine, was greatest.In the non-enzymatic system, the substituted amino acids formed reactive Schiff bases whose absorption spectra were determined. The rates of formation of these addition compounds were followed spectrophotometrically.