Purification and characterization of fungal and mammalian phosphomannose isomerases.

Phosphomannose isomerase (PMI) is essential for the production of yeast cell walls. An inhibitor which inhibits the fungal enzyme without altering the activity of the mammalian enzyme would be a potential fungicidal agent, increasingly important in view of the increasing mortality from visceral mycoses in immunosuppressed patients. We have purified human, porcine, and Candida albicans enzymes 29,000-fold to homogeneity, and characterized their physical properties, as well as their kinetic parameters, inhibition constants, and pH dependences. Surprisingly, in view of the large differences between Pseudomonas aerugenosa and Saccharomyces cerevisiae PMI, the human and C. albicans enzymes are almost identical. We suggest therefore that species-selective inhibition of the fungal rather than mammalian enzyme may require molecules which bind away from the substrate binding pocket of the enzyme.