Abstract: An improvement in a method for determining a substance present in a biological fluid by oxidizing a compound produced in the course of the determination in the presence of a dehydrogenase enzyme with the simultaneous production of reduced beta-nicotinamide adenine dinucleotide in an amount proportional to the content of the substance in the fluid, which fluid also contains an endogenous material which or a derivative of which produced during the determination likewise is oxidized in the presence of the enzyme with the simultaneous production of reduced beta-nicotinamide adenine dinucleotide, thereby interfering with the determination, which improvement involves first carrying out the oxidation-reduction reaction of the endogenous material or its derivative, then oxidizing the resulting reduced beta-nicotinamide adenine dinucleotide in the presence of lactate dehydrogenase with the simultaneous reduction of pyruvate to lactate, thereafter inhibiting the lactate dehydrogenase enzymatic activity, and thereafter

Abstract: An improvement in a method for determining glutamate oxalacetate transaminase or glutamate pyruvate transaminase present in a biological fluid, in which method L-glutamate is produced from alpha-ketoglutarate by transamination in the presence of the transaminase in the fluid, and the L-glutamate is oxidatively deaminated in the presence of glutamate dehydrogenase with the simultaneous production of reduced beta-nicotinamide adenine dinucleotide in an amount proportional to the content of the transaminase in the fluid, such fluid also containing an endogenous substance which is oxidized in the presence of glutamate dehydrogenase with the simultaneous production of reduced beta-nicotinamide adenine dinucleotide, thereby interfering with the determination.

Abstract: A colorimetric method for the determination of gamma-glutamyl transpeptidase enzyme activity in a biological fluid comprises catalytically reacting the enzyme in the fluid with a substrate of a water-soluble salt of a compound selected from the group consisting of L-gamma-glutamyl-3-sulfoanilide and L-gamma-glutamyl-4-sulfoanilide in aqueous solution to produce the corresponding aniline sulfonic acid salt as a cleavage product, diazotizing the cleavage product, and coupling the diazotized product with a coupling compound to produce a dye having a color intensity proportional to the enzyme activity.