Characteristics of glutamine uptake by two Australian Pisolithus species

Uptake of 14C-labelled glutamine by seven Australian Pisolithus isolates representing two species) was investigated over the concentration range 0.5 mmol m[minus sign]3ââ"šÂ¬Ã¢â‚¬Å“20 mol m[minus sign]3. Total uptake did not conform to simple Michaelis-Menten kinetics over this concentration range. At concentrations above 0.5 mol m[minus sign]3 much of the glutamine uptake appeared to be diffusion-like. At concentrations below 0.5 mol m[minus sign]3, subtraction of uptake in the presence of 2,4-dinitrophenol from total uptake revealed an active component that followed Michaelis-Menten kinetics. Estimated Km and Vmax values for active glutamine uptake by all isolates were in the ranges 4.0[minus sign]210 mmol m[minus sign]3 and 80[minus sign]637 nmol g[minus sign]1 d wt. min[minus sign]1 respectively. pH optima for glutamine uptake were in the ranges 4.5ââ"šÂ¬Ã¢â‚¬Å“6.0, 3.7ââ"šÂ¬Ã¢â‚¬Å“5.0 or 3.0ââ"šÂ¬Ã¢â‚¬Å“4.5, depending on the isolate. While intraspecific variation was observed, there were no apparent relationships between the two Pisolithus species and either kinetic parameters for glutamine uptake or the pH optimum for the process.