Comparison of Tryptic Peptides from the Heavy and Light Subunits of Calpain I and Calpain II by High Performance Liquid Chromatography1

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Abstract
Two different forms of Ca2+-dependent cysteine proteinase, low-Ca2+-requiring calpain I and high-Ca2+-requiring calpain II, are known to be heterodimers, each composed of one heavy (called 80K) and one light (called 30K) subunit. The most probable identity of the 30K and the substantial difference between the 80K subunits of porcine calpains I and II were clearly demonstrated by comparing the tryptic peptide maps obtained upon running a high performance liquid chromatography which permitted parallel detection of tryptophan-containing peptides by fluorometry. Comparison of the amino acid compositions of the two 30K and 80K subunits also confirmed this conclusion. The same chromatographical analysis also revealed close structural similarity of the human calpain I 30K subunit, and even some similarity existing between the calpain I 80K subunits of human and porcine origins.