A NEW PROCEDURE FOR THE PREPARATION OF HIGHLY-ACTIVE MELONIN FROM THEDRY SEEDS OF CUCUMIS-MELO L

Melon (Cucumis melo L.) dry seeds contain melonin, a protein that stro ngly inhibits ribosomes from different prokaryotic and eukaryotic sour ces including those from melon. The protein was purified by a new meth od to yield highly active and stable protein preparations that involve s chromatography through S-Sepharose Fast Flow, CM-Sepharose, Superdex 75 and Mono-S. Melonin shows important functional properties: 1) its inhibitory effects on translation were irreversible; 2) it is a single unglycosylated polypeptide chain with an apparent M(r) of 22000; 3) i t degrades RNA in a dose-dependent way without affecting DNA. In the l ight of present results melonin can be considered as a new plant RNase of unusual properties.