Abstract
The cysteine proteinase of sprouting potato tubers was purified to homogeniety as judged by PAGE or SDS-PAGE for the first time. The molecular weight of this enzyme was 28, 200 daltons by Sephadex G-75, and 27, 500 daltons by SDS-PAGE. This enzyme has an isoelectric point at pH 5.10, an optimum pH for the activity at pH 5.0-6.0, and a tendency to stability between pH 4.5-6.5. SH-compounds such as DTT (dithiothreitol) and 2-mercaptoethanol stimulated the activity of this enzyme. Heavy metal ions and Zn2+ strongly inhibited it, but EDTA slightly increased it. SH blocking reagents such as monoiodoacetate, PCMB, and TLCK inhibited this enzyme activity. Chymostatin, antipain, leupeptin and E64 caused complete inhibition.
