Enzymes of Phosphate Metabolism

Abstract

Plant tissues vary considerably in their content of protein and it may, therefore, be anticipated that some tissues, in, reference to others, may lend themselves more readily to enzyme isolation and purification. The leaves of the tapioca plant contain 20–36% of crude protein (Rogers, 1959), whereas the phylloclades of cactus have only about 7%, both on a dry weight basis (Sanwal, 1960). The nature of the nonprotein material of the starting material also influences the course of enzyme purification. The presence of mucilaginous material in tissues such as cactus interferes with conventional techniques of enzyme enrichment. Whereas, in general, the investigator is concerned with the enzyme-make up of a given tissue and preliminary screening does not find much scope, it is sometimes possible to choose a special tissue where the given enzyme is present in optimum concentration. In the animal tissue, high alkaline phosphatase activity seems to be associated with intestinal mucosa, acid phosphatase with kidney and spleen and, even more so, with prostate and 5′-nucelotidase activity with testis. Germinating seeds constitute a good sources of acid phosphatases (Newmark and Wenger, 1960). Plant tissue and microorganisms are, in general, poor sources of alkaline phosphatase, but Garen and Levinthal (1960) showed that when Escherichia coli was grown in a medium containing limiting amounts of orthophosphate, as much as 6% of the total protein synthesized was alkaline phosphatase. The availability of such a concentrated source facilitated the isolation of the phosphatase and study of its properties.