Inhibition of adenine and hypoxanthine uptake by guanosine in conidia of Neurospora crassa.

Guanosine competitively inhibits the uptake of adenine and hypoxanthine by the general purine-base permease in conidia of Neurospora crassa. There is no reciprocal effect of adenine or hypoxanthine on guanosine uptake so it is suggested that guanosine can bind to the general purine-base permease to cause this inhibition but is not transported through this system. It is known that guanosine is transported by two separate nucleoside transport sites. Guanosine also noncompetitively inhibits the specific adenine uptake system of germinating conidia.