Possible involvement of NADPH-cytochrome P450 reductase and cytochrome b5 on beta-ketostearoyl-CoA reduction in microsomal fatty acid chain elongation supported by NADPH

The addition of glucose to yeast cells activates proton efflux mediated by the plasma membrane ATPase. Accordingly, the ATPase activity of purified plasma membranes is increased up to 10-fold. The activated ATPase has a more alkaline pH optimum, better affinity for ATP and greater sensitivity to vanadate than the non-activated enzyme. All these changes are reversed by washing the cells free of glucose. This suggests two states of the ATPase which are interconverted by a covalent modification. As glucose does not affect the phosphorylation of plasma membrane polypeptides, other type of covalent modification may be involved.