Measurement of Enzyme Activity

Abstract

Most people approaching the problem of enzyme purification will be following a standard procedure for measuring enzyme activity. But in some cases, it may be useful to develop an alternative assay, for instance, a rapid spectrophotometry method to avoid queuing for the use of a scintillation counter. On rare occasions a newly discovered enzyme will need a new assay method. Ultimately the biochemist wants to know the relationship between an enzyme’s activity in vitro and its physiological situation. But the pH, ionic strength, and, particularly, the substrate concentration in vivo are likely to be quite different from the conditions used to measure the enzyme activity during a purification process. What is required here is a reliable, reproducible assay which will relate the amount of enzyme in one fraction with another, regardless of what the “activity” may mean in a physiological context.