The purification of a bovine kidney enzyme which cleaves melanocyte-stimulating hormone-release inhibiting factor.

An enzyme which catalyzes the hydrolysis of L-prolyl-L-leucylglycinamide, the factor which inhibits the release of melanocyte-stimulating hormone, was purified 189-fold from bovine kidney in a 5% yield. The molecular weight of the enzyme on gel filtration was estimated to be 300 000 and its isoelectric point was found to be pH 4.1. The single component seen on sodium dodecyl sulphate-gel electrophoresis was estimated to have a molecular weight of 56 000, indicating that the native enzyme may be a pentamer or hexamer. The enzyme could clearly be distinguished from other prolyl-cleaving enzymes.