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 capacity on the plasma membrane H+-ATPase of Penicillium simplicissimum was investigated. The activity of the H+-ATPase of the plasma membrane could be determined specifically in a subcellular fraction containing mainly plasma membranes but not in permeabilized hyphae. The maximum stimulation by glucose was two-fold after 15 min of carbon starvation. Five hours of carbon starvation did not increase stimulation of the H+-ATPase by glucose. The effect of a high extracellular buffering capacity 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 extracellular 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.