Characteristics of glutamine uptake by two Australian Pisolithus species

Uptake of 14 C-labelled glutamine by seven Australian Pisolithus isolates (representing two species) was investigated over the concentration range 0.5 mmol m −3 -20 mol m −3 . Total uptake did not conform to simple Michaelis-Menten kinetics over this concentration range. At concentrations above 0.5 mol m −3 much of the glutamine uptake appeared to be diffusion-like. At concentrations below 0.5 mol m −3 , subtraction of uptake in the presence of 2,4-dinitrophenol from total uptake revealed an active component that followed Michaelis-Menten kinetics. Estimated K m and V max values for active glutamine uptake by all isolates were in the ranges 4.0 - 210 mmol m −3 and 80 - 637 nmol g −1 d wt. min −1 respectively. pH optima for glutamine uptake were in the ranges 4.5-6.0, 3.7-5.0 or 3.0-4.5, 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.