Abstract: The present invention provides a reagent for the enzymatic determination of an enzyme substrate, containing a system for the determination of the substrate, which comprises at least one enzyme, at least one buffer substance and at least one indicator substance and optionally contains adjuvants, wherein the reagent contains a definite amount of the enzyme substrate in an insufficient amount with regard to the substrate determination capacity of the system for the determination of this substrate.The present invention also provides a process for the enzymatic determination of an enzyme substrate in the presence of disturbing substances which can react with the substrate itself or with an intermediate or end product of the indicator reaction, wherein, before the addition of the sample to be investigated, a definite amount of the substrate is first reacted with the reagent until reaction is complete, whereafter the sample to be determined is added.

Abstract: The present invention provides a process for the purification or enrichment of biologically active proteins by the addition of a selective precipitation agent, wherein an aqueous solution containing the desired protein is mixed at a pH value below its isoelectric point with such an amount of an arylsulphonic acid azo dyestuff with two sulphonate groups, which are separated from one another by 8 to 10 double bonds standing in resonance relationship, among which there is present at least one N.dbd.N double bond, that at least the greater part of the biological activity of the desired active protein is present in the precipitate, the precipitate is separated off and the active protein is again brought into solution at a pH value above its isoelectric point.

Abstract: L-lactate is quantitatively determined by the reaction thereof with nicotinamide-adenine-dinucleotide (NAD) in the presence of lactate dehydrogenase (LDH) with the formation of reduced NAD (NADH) and pyruvate, reaction of the latter with glutamate in the presence of glutamate-pyruvate-transaminase (GPT) with the formation of alanine and .alpha.-ketoglutarate in alkaline buffered solution and measurement of the NADH formed, wherein the reaction is carried out in the presence of at least 0.4 mol/liter of carbonate or bicarbonate.