Fluorometric coupled-enzyme assay for delta-aminolevulinate synthase.

The rapid and specific determination of picomole quantities of gamma-aminolevulinate has been accomplished by its enzymatic conversion to uroporphyrinogen I and subsequent fluorometric detection of the oxidized uroporphyrin I. The coupled-enzyme assay was linear with time and protein concentration and required less than 3 h for 25 individual determinations. Under the standard assay conditions, 5-100 pmol of uroporphyrin I was reliably quantitated; these values corresponded to a range of gamma-aminolevulinate synthase activities from 0.2 to 15 nmol/h/ml enzyme. The sensitivity of this method was comparable to the more time-consuming radiochemical determinations of gamma-aminolevulinate synthase activity. The gamma-aminolevulinate synthase activity of liver homogenates from uninduced rats was 8.6 U/g liver (37 degrees C).