1. Diacylglycerol kinase apoprotein was purified from membranes of Escherichia coli K12 by a six-step procedure that included HPLC. The proposed assignment of the enzyme to the dgkA gene [Lightner et al. (1983) J. Biol. Chem. 258, 10856-10861] could be supported by molecular mass determination (approximately 14 kDa), N-terminal sequencing (Met-Ala-Asn), cyanogen bromide fragmentation and amino acid analysis. As predicted, proline was absent. 2. The membrane-associated as well as the butan-1-ol-dissolved enzyme survived heating to 100 degrees C. 3. Alkylglycoside detergents were found to constitute an additional class of lipid activators. 4. The enzyme apoprotein in a non-activating substrate/detergent solution was capable of autocatalytic self-activation which was attributed to a novel feedback activation mechanism involving phosphatidic acid (diacylglycerol 3-phosphate).