Fully automated assay for cobalamin-dependent methylmalonyl CoA mutase

Abstract

We constructed a fully automated assay for the cobalamin-dependent enzyme methylmalonyl coenzyme A (CoA) mutase. The assay involves preincubation of the enzyme with adenosylcobalamin, incubation with substrate, termination of the reaction by adding trichloroacetic acid, filtration to remove precipitated protein, and finally analysis of the filtrate (containing methylmalonyl CoA and the product succinyl CoA) by HPLC. These steps were carried out by an inexpensive programmable autosampler equipped with thermostated sample racks and mobile disposable extraction column racks used here as a sample filtering device. A central element in the developmental work was to measure stability of reagents, enzyme, and product against the storage conditions during unattended analysis and the time table of the program. We evaluated the performance of the method by measuring methylmalonyl CoA mutase activity in rat liver, human fibroblasts, and human glioma cells. The within-run imprecisions (CV) were 2-10% for measuring enzyme activity in 20 replicate samples of a homogenate (test of the automated assay), and 7-12% for measuring enzyme activity in homogenates from 20 culture dishes (test of the total procedure). The method allows the unattended analysis of 56 samples per 24 h. This strategy for automation may be easily adapted for other enzyme assays.