PROTEINASE-K PROCESSING OF RABBIT MUSCLE CREATINE-KINASE

Proteinase K cleaves selectively both cytosolic and mitochondrial isof orms of creatine kinase leading to the appearance of two fragments, a large N-terminal one (K1) and a small C-terminal peptide (K2) which re main associated together. The loss of enzymatic activity correlates wi th the extent of monomer cleavage. N-terminal sequencing of the K2 fra gments from rabbit cytosolic and pig mitochondrial creatine kinase sho ws that these peptides begin with A(328) and A(324), respectively. Ele ctrospray ionization mass spectrometry demonstrates that K2 peptide is composed of 53 residues (A(328)-K-380). However, the C-terminal end o f the K1 fragment is not A(327) as expected, but D-325. Thus, the amin o acids residues T-326 and A(327) have been eliminated by the protease .