CIRCULAR-DICHROISM OF STEM BROMELAIN - A 3RD SPECTRAL CLASS WITHIN THE FAMILY OF CYSTEINE PROTEINASES

Two forms of stem bromelain (EC 3.4.22.4) were isolated from commercia l, crude and chromatographically purified preparations of the enzyme b y means of gel-filtration and cation-exchange liquid chromatography. T hese forms possess nearly identical secondary and tertiary structures, as judged from their circular dichroism (c.d.) spectra. The spectral characteristics of stem bromelain suggest that this enzyme belongs to the alpha + beta protein class, as other cysteine proteinases do. In a greement with these results, quantitative estimation of secondary stru ctures yielded amounts similar to those for papain and proteinase Omeg a. However, the bromelain c.d. curve is clearly distinguishable from t hose reported for papain and proteinase Omega, on one hand, and that o f chymopapain, on the other. Thus it is apparent that there are at lea st three types of c.d. spectra associated with the family of cysteine proteinases.