A problem in the radiochemical assay of glucose-6-phosphatase in muscle.

A radiochemical assay for glucose-6-phosphatase, which depends on the absorption of radiolabelled substrate on to a nascent precipitate of BaSO4 and Zn(OH)2, can give rise to erroneously high activities. Adsorption on to a Fe(OH)3 precipitate does not expose the incubation medium to extreme alkaline conditions and provides a satisfactory and simple assay. This method demonstrates a very low activity of the enzyme in mammalian muscle, in contrast with previous findings.