The activator-binding sites within the C1 domains of protein kinase C (PKC) are also able tobind alcohols and anesthetics. In this study, the nature of the interaction of these agents with the hydrophobicregion within the C1 domains was investigated and a structure-activity relationship for the alcohol effectswas obtained. The effects of a series of
n-alkanols on PKC
activity, determined using an in vitro assaysystem that lacked lipids, were found to be a nonlinear function of the chain length. In the absence ofphorbol ester or diacylglycerol, 1-octanol potently
activated PKC
in a concentration-dependent manner,while 1-heptanol was completely without effect, despite differing by one methylene unit. The minimalstructural requirement for the activating effect corresponded to R-CH(OH)-(CH
2)
n-CH
3, where R = Hor an alkyl group and
n 6. Consistent with this, 2-octanol, for which
n = 5, was without effect on theactivity, even though this alcohol is only marginally less hydrophobic than 1-octanol, whereas 2-nonanol,for which
n = 6, was able to produce activity. Importantly, it was found that PKC
was activated to agreater extent by
R-2-nonanol than by the
S enantiomer. The potentiation of phorbol ester-induced,membrane-associated PKC
activity by long-chain
n-alkanols reported previously (
Slater, S.
J., Kelly,M. B., Larkin, J. D., Ho, C, Mazurek, A, Taddeo, F. J., Yeager, M. D., Stubbs, C. D. (1997)
J. Biol.Chem. 272, 6167-6173), was also found here for nonmembrane associated PKC, indicating that thiseffect is an intrinsic property of the enzyme rather than a result of membrane perturbation. Overall, theresults suggest that the alcohol-binding sites within the C1 domains of PKC
contain spatially distincthydrophilic and hydrophobic regions that impose a high degree of structural specificity on the interactionsof alcohols and other anesthetic compounds, as well as diacylglycerols and phorbol esters.