Some properties and behaviour of alkaline inorganic pyrophosphatase of corn (Zea mays) endosperm during germination

Abstract

Summary 1. Crude homogenate of the endosperm of germinating corn seeds contain two enzymes hydrolyzing inorganic pyrophosphate. One of these enzymes, optimum pH 5, requiring no Mg2+ ions, with low substrate specificity, seems to be an acid inorganic pyrophosphatase. The second enzyme, optimum pH 8.7, requiring Mg2+ ions as activators and substrate components (MgPPi), with optimum ratio MgCl2/PPi = 8, exhibits the properties of alkaline inorganic PPase. 2. Changes in the inorganic PPase activity and soluble protein content in the endosperm of developing seeds were determined, beginning from dry seeds till the 10 th day of germination. The enzyme activity and soluble protein content increased to reach a maximum on the 5th day of germination, whereupon they dropped. Cycloheximide reduced both the PPase activity and soluble protein concentration. 3. The degree of polymorphism of PPase during seed development was investigated by disk electrophoresis. Both qualitative and quantitative differences in the degree of polymorphism were found; the greatest number of bands with PPase activity, with Rf 0.43, 0.53, 0.61, 0.69, respectively, was observed between the 3rd and 5th day of germination. 4. The possible role of inorganic PPase and of its isoenzymes in the processes of plant development were discussed.