A simplified method for the measurement of gamma-butyrobetaine hydroxylase activity

A method for the assay of gamma-butyrobetaine hydroxylase activity is described. The procedure is based on the measurement of 3H2O formed from [2,3-3H]gamma-butyrobetaine. The formation of 3H2O was essentially linear with time of incubation and enzyme concentration. Despite a significant isotope effect that causes the extent of hydroxylation to be underestimated, an appropriately determined correction factor permits one to relate quantitatively the degree of detritiation to the amount of carnitine formed. The assay is simple, rapid, specific, accurate, highly reproducible, and relatively sensitive. Its reliability and convenience represent an improvement over existing methods based on the tedious and time-consuming enzymatic radioisotopic determination of the carnitine formed or on the coupled decarboxylation of [1-14C]alpha-ketoglutarate, a method that cannot be used in crude extracts.