Inactivation of Calpain I and Calpain II by Specificity-Oriented Tripeptidyl Chloromethyl Ketones

抄録

Three new tripeptidyl chloromethyl ketones, Leu-Leu-XCH₂Cl, with X representing Phe, Tyr, or Lys, were synthesized and their potencies to inactivate calpains I and II were compared. They were designed to fulfil the specificity requirement of cal-pains established recently. When compared in terms of the dose for 50% inactivation, Leu-Leu-PheCH₂Cl was the strongest inactivator, being 500-600 times more effective than tosyl-PheCH₂Cl and 5-14 times more than N-[N-(L-3-trans-carboxyoxiran-2-carbonyl)-L-leucyl] agmatine (E-64). The potency toward calpain, either I or II, decreased in the order Phe>Tyr>Lys derivatives>E-64, whereas that toward papain was E-64>Lys>Phe>Tyr derivatives. From the determined kinetic parameters, the Phe derivative was 18.3 and 16.6 times more effective than E-64 on calpains I and II, respectively. Likewise, the rate of the alkylation reaction by these chloromethyl ketones with calpain I was 2-4 times greater than that with calpain II. Leu-Leu-PheCH₂Cl and its N-dansylated product should be useful for highly selective affinity labeling of calpains I and II.