THE IN-VIVO EFFECT OF GLUCOSE AND EXTRACELLULAR PH ON THE PLASMA-MEMBRANE H-ATPASE OF PENICILLIUM-SIMPLICISSIMUM()

The in vivo effect of glucose and a high extracellular buffering capac ity on the plasma membrane H+-ATPase of Penicillium simplicissimum was investigated. The activity of the H+-ATPase of the plasma membrane co uld be determined specifically in a subcellular fraction containing ma inly plasma membranes but not in permeabilized hyphae. The maximum sti mulation by glucose was two-fold after 15 min of carbon starvation. Fi ve hours of carbon starvation did not increase stimulation of the H+-A TPase by glucose. The effect of a high extracellular buffering capacit y was investigated at pH 6 and 7.5. At pH 7.5, the H+-ATPase activity was slightly decreased, whereas at pH 6 it was slightly increased, In summary, neither the presence or absence of glucose nor the extracellu lar pH led to gross changes in the HC-ATPase activity. A relationship between the activity of the H+-ATPase and buffer-stimulated excretion of citrate could not be detected.