Quantitative assay of enzymes in tissues

Abstract

The purpose of emphasizing the difficulties involved in the assay of enzymes in tissues is to point out that the methods developed for the assay of purified enzymes cannot be applied without modification to the assay of the enzymes in a tissue homogenate. Proper attention must be given to the preparation of the tissue and indiscriminate deep freezing is to be avoided. Provided the conditions are chosen so that the reaction is linear over the period of assay, methods which are relatively simple to perform can be devised for the assay of most of the enzymes of interest in metabolic defects. The finding of absent or low activity of one enzyme together with a normal activity of other enzymes in the same sequence is sufficient to show the cause of the metabolic abnormality. This does not establish in itself whether the enzyme protein has been completely deleted or whether there is a normal amount of enzyme protein with an abnormal structure. The presence of enzymes with abnormal Km values in some instances of metabolic block suggests that the second possibility may sometimes be the case. For this reason it is interesting to study the properties of the enzyme as well as measuring its activity. It is often necessary to assay several enzymes of a metabolic sequence under inve3tigation, not only to prove that one defective enzyme activity exists, but that other enzymes of the series are normal.