myo-Inositol-1-phosphatase from bovine brain was purified over 2000-fold. The native enzyme has a Mr of 59,000, and on SDS/polyacrylamide-gel electrophoresis the subunit Mr was 31,000. Thus the native enzyme is a dimer of two apparently identical subunits. The enzyme, purified to a specific activity of more than 300 units/mg of protein (1 unit of enzyme activity corresponds to the release of 1 mumol of Pi/h at 37 degrees C), catalysed the hydrolysis of a variety of phosphorylated compounds, the best one, in terms of V/Km, being D-myo-inositol 1-phosphate. Kinetic constants of compounds tested, including both isomers of glycerophosphate and two deoxy forms of beta-glycerophosphate, were measured. They show the importance of the two hydroxyl groups which are adjacent to the phosphate in myo-inositol 1-phosphate. With a wide variety of substrates Li+ was found to be an uncompetitive inhibitor whose Ki varied with substrate structure.

2-(4-Amino-4-carboxybutyl)aziridine-2-carboxylic acid (3) (aziridino-DAP) was identified as the product of spontaneous hydrolysis of alpha-(halomethyl)diaminopimelic acids (alpha-halomethyl-DAPs) 2a-c. Under physiological conditions, 3 is an extremely potent irreversible inhibitor of the bacterial enzyme diaminopimelic acid epimerase (DAP-epimerase; EC 5.1.1.7). This unusual mode of action of an alpha-halomethyl amino acid with a non-pyridoxal enzyme is investigated. Synthesis and characterization of 2a-c and 3, kinetics of spontaneous formation of 3 from alpha-halomethyl-DAPs, and kinetics of enzyme inhibition by both 3 and by alpha-halomethyl-DAPs are reported.