Addition of glucose and other sugars to derepressed cells of the fungus var. triggered activation of the plasma membrane H-ATPase within 5 min. Glucose was the best activator while galactose and lactose had a lesser effect. The activation was not prevented by previous addition of cycloheximide and it was fully reversible when the glucose was removed. The activation process also caused changes in the kinetic properties of the enzyme. The non-activated enzyme had an apparent of about 3.2 mM for ATP whereas the activated enzyme showed an apparent of 0.26 mM. In addition, the pH optimum of the H-ATPase changed from 6.0 to 7.5 upon activation. The activated enzyme was more sensitive to inhibition by vanadate. When was cultivated in media containing glucose as the major carbon source, enhanced H-ATPase activity was largely confined to the period corresponding to the lag phase, i.e. just before the start of acidification of the medium. This suggests that the activation process might play a role in the onset of extracellular acidification. Addition of glucose to var. cells also caused an increase in the cAMP level. No reliable increase could be demonstrated for the other sugars. Addition of proton ionophores such as DNP and CCCP at pH 5.0 caused both a large increase in the intracellular level of cAMP and in the activity of the plasma membrane H-ATPase. Inhibition of the DNP-induced increase in the cAMP level by acridine orange also resulted in inhibition of the activation of plasma membrane H-ATPase. These results suggest a possible causal relationship between the activity of var. plasma membrane H-ATPase and the intracellular level of cAMP.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error