Quantitative assay of enzymes in tissues.

There are two main groups of conditions in which the determination of enzyme activities in tissues is necessary or desirable. They are (a) primary defects of enzyme synthesis and (b) alterations of enzyme activity secondary to damage of the cell. Since the time of Garrod, hereditary metabolic disorders have been recognized to be due to a defect of one or perhaps more enzymes, which may have farreaching metabolic consequences and produce multiple biochemical and other abnormalities. This communication is confined to enzyme assays using tissues from organs such as liver, kidney, or gastrointestinal mucosa and including the leucocytes of the blood. It excludes the examination of blood plasma, the enzymes of which are, of course, not synthesized there, but accumulate by leakage from the organs it bathes or from degradation of red and white blood cells. A general review of methods of enzyme assay is not attempted, but the principles of the methods used for individual enzyme assays are *emphasized. Selection has been based on the special factors which must be taken into account in this field, eg, the limited amount of material available so that the sensitivity of a method is important, and the fact that tissues contain a mixture of enzymes as well as many different substrates. The methods of assay available for pure enzymes are not always applicable to a crude tissue homogenate.