Activation of C₅₅ isoprenoid alcohol phosphokinase from Staphylococcus aureus. I. Activation by phospholipids and fatty acids

C₅₅ Isoprenoid alcohol phosphokinase is one of a few intrinsic membrane proteins which have been purified to homogeneity. This enzyme, isolated for Staphylococcus aureus H membranes, catalyzes the ATP dependent phosphorylation of C₅₅ isoprenoid alcohols. The properties of the enzyme are those one might expect of an intrinsic membrane protein. It has an unusually high content of nonpolar amino acids (58%): it is insoluble in water, but soluble in organic solvents such as 1 butanol. One of its substrates is highly lipophilic, and the enzyme activity is absolutely dependent on the presence of a lipid activator. The exceptional stability of this enzyme both in the presence and absence of lipids makes this system attractive for studying lipid protein interactions. The activation of C₅₅ isoprenoid alcohol phosphokinase by a variety of lipids has been investigated. A number of amphipathic lipids can serve as effective kinase activators. Both the nature of the polar and nonpolar groups are important, but kinase activation does not depend on any particular chemical structure or charge on the lipid. The structure of those lipids which are most effective, as well as an analysis of their temperature profiles, suggests that bulk physical properties are significant. Lipids which provide a hydrated loosely packed, highly fluid environment are often effective activators.