Summary ADVANCES IN CLINICAL CHEMISTRY

Under most circumstances the enzyme contents of different samples of serum, plasma, etc., can be compared quantitatively only in terms of their respective catalytic activities, i.e., by the relative effects which equal volumes of the different samples have on the rate of the specific chemical reaction catalyzed by the enzyme in question. Thus, in contrast to what is usually the case for other types of analysis, enzyme assays always imply the measurement of reaction rates; that is to say, the amount of chemical change produced in a defined interval of time in the presence of a known volume of the solution of the enzyme. Since the rates of enzyme- catalyzed reactions are markedly dependent upon several variables- notably pH and temperatur-these must also be strictly controlled. The need to measure time intervals accurately and to control variables, such as temperature, introduces constraints into the design of automatic en- zyme analyzers that do not apply with the same rigor to analyzers in- tended for nonenzymic determinations. The initial rate of a reaction cataly