Determination of phosphorus-32 and -33 in aqueous solution

Sensitive, nonradioactive assay of phosphorylase kinase through measurement of enhanced phosphorylase activity towards fluorogenic dextrin

Glycogen phosphorylase (GP) exists in two interconvertible forms, GPa (phosphorylated form, high activity) and GPb (nonphosphorylated form, low activity). Phosphorylase kinase (PhK) catalyses the phosphorylation of GPb and plays a key role in the cascade system for regulating glycogen metabolism. In this study, we developed a highly sensitive and nonradioactive assay for PhK activity by measuring the enhanced GP activity towards a pyridylaminated maltohexaose. The enhanced GP activity (ΔA) was calculated by the following formula: ΔA = A(+) - A(0), where A(+) and A(0) represent the GP activities of the PhK-treated and PhK-nontreated samples, respectively. Using a high-performance liquid chromatograph equipped with a fluorescence spectrophotometer, the product of GP activity could be isolated and quantified at 10 fmol. This method does not require the use of any radioactive compounds and only 1 µg of GPb per sample was needed to obtain A(+) and A(0) values. The remarkable reduction in GPb concentration enabled us to discuss an interesting new role for glycogen in PhK activity.

The use of Cerenkov radiation for monitoring reactions performed in minute volumes: examples from recombinant DNA technology

A method in which minute volumes of initially unknown size are used to monitor reactions has been developed. It is applicable whenever 32P-labeled substrates can be distinguished from 32P-labeled products by a filter assay. Three determinations are required: the Cerenkov radiation emitted (1) by the unknown aliquots affixed to filters and dried; (2) by the identical filters after processing to remove either substrates or products; and (3) by a precisely measured, necessarily much larger, aliquot in solution. Given the value obtained in (3) and the efficiency with which Cerenkov radiation can be detected in the dry state (25%) compared with the liquid state (56%), the unknown volumes, together with their acid-insoluble radioactivity, can be calculated from (1) and (2), respectively. Since the known volume counted in solution is not lost to further manipulations, the entire procedure uses less than 0.5 microliter.