ABSTRACT
We have demonstrated simultaneous existence of progesterone receptors and GTPase activity in the membranes prepared from the filamentous fungus Rhizopus nigricans. The results obtained with pertussis toxin treated fungal mycelium suggest that these receptors do not couple to Gi-Go-proteins and play a role in the induction of steroid hydroxylating enzyme system by steroid substrates in the fungus.
Subject(s)
GTP-Binding Proteins/metabolism , Receptors, Progesterone/metabolism , Rhizopus/metabolism , Binding, Competitive , Cell Membrane/metabolism , Dose-Response Relationship, Drug , GTP Phosphohydrolases/metabolism , Progesterone/pharmacology , Receptors, Progesterone/classificationABSTRACT
Peptitergent PD1 shows complex effects on GTPase activity of rat brain cortical membranes: inhibition in the presence of lower concentrations of GTP and activation at a higher concentration, above 0.5 microM, of GTP. Its effect is dose dependent and is characterized by an EC50 of 1.8 +/- 0.2 microM and a Hill coefficient of 1.6 +/- 0.3, and it increases both Km and Vmax of the GTP hydrolysis. PD1 that was unable to solubilize G-proteins from the membranes probably acts on them by direct binding near the C-terminal alpha-helical region of the Galpha subunit, similarly to mastoparan.
