Properties of Barrier, a novel Saccharomyces cerevisiae acid protease.

We have studied the specificity of Barrier, a protease secreted by Saccharomyces cerevisiae, towards its natural substrate alpha-factor, a tridecapeptide mating pheromone. Sub-fragments of alpha-factor synthesized or prepared by cyanogen bromide cleavage and a related pheromone from Saccharomyces kluveri were studied as potential substrates or competitive inhibitors. None of the tested peptides was a potent inhibitor or substrate for Barrier. Barrier shares extensive sequence similarity to the active site residues of aspartyl proteases but universal irreversible inhibitors of this class of enzymes failed to inactivate Barrier, suggesting that it is a novel fungal aspartyl protease.