Histidine2 of the alpha-factor of Saccharomyces cerevisiae is not essential for binding to its receptor or for biological activity.

Seven His2 analogs of the Saccharomyces cerevisiae [Nle12]alpha-factor, WXWLQLKPGQP(Nle)Y, where X = beta-D-thienylalanine, beta-L-thienylalanine, 1-D-methylhistidine, 1-L-methylhistidine, 3-D-methylhistidine, 3-L-methylhistidine, and beta-3-L-pyridylalanine, were synthesized and purified to homogeneity. Assays were carried out on binding to the alpha-factor receptor and of biological activity determined by either growth arrest or morphological changes in target cells. In the L-isomer, replacement of the imidazole of histidine by thiophene or 3-pyridyl groups or derivatization of either nitrogen of the imidazole ring by methylation resulted in a 2-100-fold decrease in bioactivity. D-Isomers of the beta-thienylalanyl-, 1-methylhistidinyl-, or 3-methylhistidinyl-alpha-factors did not possess measurable bioactivity with the exception of comparatively low activity of the 3-D-methylhistidinyl and 1-D-methylhistidinyl-alpha-factors in the morphogenesis assay. In contrast, both active and inactive analogs demonstrated binding affinities 10-20-fold less than that of [Nle12]alpha-factor. These results indicate that the histidine residue of alpha-factor is not required for binding to the receptor or for biological activity and that bioactivity and binding can be dissociated through the use of pheromone analogs.