The interaction of pyrene labeled diacylglycerol with protein kinase C in mixed micelles

The binding of protein kinase C (PKC) to pyrene-labeled diacylglycerol (pDG) has been studied in a mixed micellar system by monitoring resonance energy transfer from excited tryptophans to pyrene with time-correlated single photon counting. The average lifetime of the excited state of the tryptophans in PKC showed a clear dependence on the mole percentage pDG in micelles in contrast with pyrene-labeled phosphatidylcholine (pPC). The binding data has been analyzed to a simple model which encompasses the size of the micelles and the binding constant of the pDG-PKC complex. From our data, though, these quantities cannot be determined independently. If we have no size information on the micelles we can determine a lower boundary of this quantity compatible with the data. When the micellar size is known, a binding constant for the DG-PKC complex can be extracted. The presented analytical approach can be applied to other systems in which lipid-protein interactions must be quantified.