The present proposal describes experiments designed to determine the mode of action of the metabolic regulator 3,4-dihydroxybutyl-l-phosphonate. This compound has profound effects on phospholipid metabolism and is incorporated into chloroform soluble material(s) in vivo and in vitro. These materials will be characterized and the enzyme(s) responsible for their synthesis identified. Attempts will be made to prepare derivatives of the phosphonic acid that will be permeable to cell membranes and to isolate bacterial mutants that are resistant to 3,4-dihydroxybutyl-l-phosphonate. Biological systems will be screened for the ability to use the 3,4-dihydroxybutyl-l-phosphonate in place of glycerol-3-phosphate in the biosynthesis of a phosphonic acid analog of phosphatidic acid.