Effects of phospholipid headgroup and phase on the activity of diacylglycerol kinase of Escherichia coli

Diacylglycerol kinase (DGK) of Escherichia coli has been reconstituted into a variety of phospholipid bilayers and its activity determined as a functi on of lipid headgroup structure and phase preference. The anionic phospholi pids dioleoylphosphatidic acid, dioleoylphosphatidylserine, and cardiolipin were all found to support activities lower than that supported by dioleoyl phosphatidylcholine. In mixtures of dioleoylphosphatidylcholine and 20 mol % anionic phospholipids, the presence of anionic phospholipids all resulted in lower activities than in dioleoylphosphatidylcholine, except for dioleo ylphosphatidylglycerol whose presence had little effect on activity. In som e cases, the low activity in the presence of anionic phospholipid followed from a decrease in v(max); in some cases, it followed from an increase in t he K-m for diacylglycerol, and in the case of dioleoylphosphatidic acid, it followed from both. Activities in mixtures containing 80 mol % dioleoylpho sphatidylethanolamine were lower than in dioleoylphosphatidyleholine at tem peratures where both lipids adopted a bilayer phase; at higher temperatures where dioleoylphosphatidylethanolamine preferred a hexagonal Hn phase, the differences in activity were greater. These experiments suggest that the p resence of lipids preferring a hexagonal Hit phase leads to low activities. Activities of DGK are low in a gel phase lipid.