Spectrophotometric Determination of Affinities of α‐Factors for Their G Protein‐Coupled Receptors in Saccharomyces cerevisiae

This is the authors' abstract. We don't add key points for this paper.

A new and relatively simple spectrophotometric technique has been developed for the accurate determination of α‐factor pheromone affinities for Ste2p whole cell receptor in yeast a‐cells. We designed and tested nine detector peptides containing mono‐ (ε412 = 14 500) or tri‐cysteine residues (ε412 = 43 660). The free unbound detector was detected using Ellman's reagent at 412 nm. Saturation binding studies using Saccharomyces cerevisiae Y 7925 ( MATa ) at a concentration of 2.5 × 1011 cells/mL with the highest affinity detector 1, [Orn6]α‐factor‐[Cys]3, resulted in a dissociation constant ( K D ) of 1.67 × 10−7 and total binding sites per cell (B cell = 29 500 sites/cell) comparable with those obtained using radiolabeled binding assays. Competitive binding assay using five nonchromogenic α‐factor analogs allowed for the determination of each K D value. [Orn6,d‐Ala9]α‐factor showed the highest receptor affinity ( K D = 1.03 × 10−7 M), which was threefold higher than that of native α‐factor. This assay provides rapid and convenient results for determining the relative affinities of nonchromogenic α‐factors and eliminates the need for radioactive waste disposal.