Evidence from two-protonic-state reactivity probe kinetics that chymopapain in fresh nonfruit latex ofCarica papaya consists of multiple forms of chymopapain A. The value of catalytic site characteristics in the identification, classification, and characterization of the papaya cysteine proteinases papain, the chymopapains, and papaya proteinase Ω

Abstract

Fresh latex ofCarica papaya was collected from the stem, leaves, and petioles of the growing plant and fractionated by ion-exchange chromatography on a column of SP-Sephadex-C50 and by FPLC using a Mono S column. The fractions were examined for catalytic activity using Z-Lys-ONp andl-BAPNA as substrates and the thiol contents and reactivity characteristics were determined by using 2,2′-dipyridyl disulfide as a two-protonic-state thiol titrant and reactivity probe. By these methods the fresh nonfruit latex was shown to contain papain (EC 3.4.22.2), multiple forms of chymopapain, all of which have catalytic site reactivities characteristic of chymopapain A, and papaya proteinase Ω (originally called papaya peptidase A). The necessity now to characterize the catalytic site of a chymopapain in order to identify it is discussed.