A method for measuring serum glutamic oxalacetic transaminase activity is described, in which substrate concentrations are more nearly optimal than in previous colorimetric methods. By coupling the diazonium salt at a pH of 4.2, interference from α-oxoglutarate is negligible. Oxalacetate is produced at a linear rate to 180 I.U. Results correlate well with those obtained by a reference spectrophotometric method.
An enzymic rate method for measuring beta-hydroxybutyrate in plasma by use of beta-hydroxybutyrate dehydrogenase (EC 1.1.1.30) was adapted to the Roche COBAS-BIO centrifugal analyzer. Optimum reagent composition and reaction conditions were determined, to provide increased sensitivity and accuracy. Use of magnesium ions increased sensitivity. Comparison of results with those of a manual enzymic endpoint method involving perchloric acid protein-free filtrates of whole blood showed excellent correlation (r = 0.996). The method has good within-run and day-to-day precision. Linearity of the standard curve extends to 5000 mumol of beta-hydroxybutyrate per liter. The assay can be completed in less than 5 min and requires 15 microL of plasma and minimal reagent volumes.
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