Enzymes purity criteria

The purity of the enzyme is reflected by its specificity for a panel of substrates. Many preparations may contain contaminating activities and the number of crystallizations indicated for commercial preparations is a poor criterion for purity. The absence of proteases is important to maintain maximum stability of the preparations. Contaminating microorganisms very often produce proteases however, the addition of preservatives may interfere with enzyme activity. For example, POase is extremely sensitive to both contaminating bacteria and NaNs, Sometimes, enzymes can be stabilized by the addition of substrate homologues. 

Electrofocus sing is now established as the best method for resolution and analysis of proteins, including enzymes, and is considered as the standard criterion of purity for proteins. 

The ratio of the activities of a lipolytic enzyme toward the SM-I and sn-3 acyl enantiomers is representative for its stereopreference under given conditions and can be taken as a criterion for enzyme identity and/or purity. Figure 4 shows a comparison of stereropreferences thus obtained for various lipases purchased from different companies. The lipases from Mucor javanicus exhibit very similar values and have most likely been produced by the different manufacturers in similar quality. In contrast, the stereopreferences of two lipases from Mucor mihei and Chromobacterium viscosum differ significantly depending on the industrial source. 

The problem of receptor isolation and purification Is very much more difficult than the problem of enzyme Isolation and purification. Since an enzyme "does something", its activity provides a criterion of purity. On the other hand, receptors, apart from their ability to "receive" small molecules, have no activity which can be measured readily. 

These results leave an element of uncertainty because miuntenance of constant specific radioactivity on recrystallization is not an infallible criterion of radioactive purity. The authors were unable to find a system of paper chromatography that separated glutamic acid from a-aminoadipic acid. Added to this is the fact that Schweet et al. (10) could find no radioactivity in a-aminoadipic acid added as a trapping agent to cultures of Neurospora metabolizing labeled ly ne, and Suda et al. (169) found no formation of this compound in a bacterial enzyme system that oxidized Ijrsine to 5-aminovaleric acid. 

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