DETERMINATION OF PRECURSORS TO URINARY METHYL-MALONIC ACID IN MAN - MEASUREMENT OF URINARY EXCRETION AND SPECIFIC ACTIVITY

A method is described for the determination of urinary methylmalonic acid and its specific activity following the administration of 14C-labeled precursors to humans. The method involves ether extraction, anion exchange column chromatography and colorimetric determination of the separated methylmalonic acid, after coupling to diazotized p-nitroaniline. Specific activity determination includes liquid scintillation quantitation of the 14C content after further purification of the methyl-malonic acid fraction by thin-layer chromatography. Analytical losses were corrected for by use of 3H-labelled methylmalonic acid. Day to day analytical variance and recovery data are presented. Increased methylmalonic acid urinary excretion was noted in all vitamin B12-deficient subjects. While there was 14C incorporation into urinary methylmalonic acid after intravenous administration of [2-14C] propionate in both a normal subject and in a vitamin B12-deficient patient, a much larger fraction of the injected dose appeared in the urinary methylmalonic acid of the vitamin B12-deficient patient. © 1968.