Preparation of homogeneous crystals of myo-inositol 1-phosphate synthase from rat testicles--further data on the chemical and catalytic properties of the enzyme (studies on the biosynthesis cyclitols, XXXIX).

Pre-purified preparations of myoinositol-1-phosphate synthase (E.C. 5.5.1.4) from rat testes can be purified to homogeneity by first crystallizing the enzyme according to JAKOBY and then recrystallizing it at a pH value close to the isoelectric point while slowly increasing the temperature from 0 to 15 degrees C. This method gives a much yield of homogeneous enzyme than the previously used purification by affinity chromatography. It was further found that the pure enzyme contains close to 2 mol NAD+ per mol enzyme; it does not contain any metal. At substrate saturation the enzyme binds close to 1 mol substrate per mol enzyme, as determined by using radioactively labelled substrate and binding it to the enzyme by reduction with NaBH4. The reaction catalyzed by the enzyme is irreversible.