Crystallization and preliminary X-ray analysis of a protease inhibitor from the latex of Carica papaya.

A Kunitz-type protease inhibitor purified from the latex of green papaya (Carica papaya) fruits was crystallized in the presence and absence of divalent metal ions. Crystal form I, which is devoid of divalent cations, diffracts to a resolution of 2.6 A and belongs to space group P3(1) or P3(2). This crystal form is a merohedral twin with two molecules in the asymmetric unit and unit-cell parameters a = b = 74.70, c = 78.97 A. Crystal form II, which was grown in the presence of Co2+, diffracts to a resolution of 1.7 A and belongs to space group P2(1)2(1)2(1), with unit-cell parameters a = 44.26, b = 81.99, c = 140.89 A.