Specific binding sites for human luteinizing hormone in Neurospora crassa and Saccharomyces cerevisiae

Specific binding sites for ¹²⁵I-labelled human luteinizing hormone (hLH) were detected in microsomal and cytosolic fractions from Saccharomyces cerevisiae, Neurospora crassa and a wall-less (‘slime’) mutant of N. crassa. Scatchard analysis of hLH-binding to microscomes revealed the presence of both high affinity (K_a of 60–70 × 10¹⁰m⁻¹) and lower affinity (K_a of 1·3–1·9 × 10¹⁰m⁻¹) binding sites in each organism. ¹²⁵I-hLH binding to both S. cerevisiae and N. crassa (wild type) microsomes was inhibited by low concentrations of Ca²⁺ and Mg²⁺ (30 μm), and by higher concentrations of Na⁺ and K⁺ (40 mm). Binding was also inhibited, in dose-dependent fashion, by partially-purified preparations of hLH and hCG. In contrast, highly purified hCG preparations were much less potent, though they strongly inhibited hLH binding to sheep corpus luteum LH-receptors. Moreover, high-purified hCG β-core protein inhibited hLH binding to S. cerevisiae and N. crassa microsomes in a dose-dependent manner, but had no effect on hLH binding to sheep luteal receptors. The properties of the S. cerevisiae and N. crassa LH-binding sites are similar to those of binders detected previously in Candida albicans. Thus, interactions between hLH-like molecules and their receptors may have a widespread distribution in the Ascomycotina and Deuteromycotina.