The effects of a variety of inhibitors suggested that the promastigote surface protease (PSP) of Leishmania might be a Zn metalloprotease. To investigate this possibility, at. emission and absorption spectroscopic analyses were conducted which showed that PSP contains 1 atom of Zn per 63-kilodalton (kDa) monomer. Further studies showed that the enzyme could be biosynthetically labeled with 65ZnCl2. The comparison of the amino acid sequence of L. major PSP with 9 other Zn metalloproteases revealed significant similarity in the area of their Zn-binding sites. These data showed clearly that the promastigote surface protease of Leishmania is a Zn metalloprotease. Secondary structure anal. by CD spectroscopy indicated that PSP contained >40% b-strand and <20% a-helical structure. The mol. wts. of amphiphilic PSP (152 kDa) and of hydrophilic PSP (142 kDa), detd. by quant. electron scattering, suggested that the purified enzyme occurs in soln., and presumably at the cell surface, as a noncovalent homodimer. [on SciFinder (R)]