Two pathways in the biosynthesis of cadystins (γEC)nG in the cell-free system of the fission yeast

Abstract

Small metal-binding peptides, cadystins, with the general structure of (gamma-Glu-Cys)n-Gly ((gamma EC)nG), were synthesized in a cell-free system of fission yeast to examine the in vivo synthetic pathway. The crude enzyme for cadystin synthesis was prepared by ammonium sulfate precipitation (75% saturation) from the 120,000 x g supernatant of the cell extract, and the excess salt in the enzyme fraction was removed by Sephadex gel filtration. Using this crude enzyme fraction, it was shown that there were two pathways for cadystin biosynthesis. One pathway is gamma-Glu-Cys (gamma EC) dipeptidyl transfer from both glutathione (gamma ECG) and cadystins to glutathione and cadystins. The other one is gamma EC polymerization from (gamma EC)n and glutathione to (gamma EC)n + i, followed by glycine addition with glutathione synthetase.