Stability Test of Six Enzymes for Internal Quality Control

Abstract

The daily quality control for the determination of the catalytic activity concentrations of enzymes is an important aspect in clinical chemistry. Instead of the expensive, commercially available control sera, we have looked for a simple, reliable and cheap method for the quality control of enzyme determinations. Commercially available enzymes were suspended in an albumin solution and ampoules were filled with 1.0 ml of these various solutions. The ampoules were stored at 4 °C or-20 °C. Once a week, during 10 months, catalytic activities of these enzyme-albumin solutions were determined together with the same activities in freshly reconstituted control sera. Aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, creatine kinase and y-glutamyltransferase were determined at 30 °C according to well-described methods. a-Amylase was determined with the Phadebas method at 37 °C. Except for creatine kinase, the stability and reliability of these enzyme solutions are fully comparable with control sera during the experimental period. The catalytic activity concentration of creatine kinase decreased slowly during the 10 months. The enzyme solutions react in the same manner as commercial test sera on changes in the reaction conditions for the enzyme determinations. The conclusion seems justified that these enzyme solutions can be used for the daily quality control of the enzyme determinations instead of control sera.

Long-Term Stability of Enzymes in Human Serum Stored in Liquid Nitrogen

“…Therefore, a considerable increase of oxidized glutathione at this storage temper ature and of glutathione reudctase in the sam ple stored at -196 °C is not to be taken into account. It is more likely that the instability of CK could be due to the absence of sulfhydryl compounds in the stored samples [10], A sim ilar result of CK instability was obtained at -20 °C [5], Perhaps better stability can be attained by adding sulfhydryl compounds or chelating agents [12].…”

“…Hafkenscheid and Van der Ven-Jongekrijg [5] proposed another interesting and reliable substitute for commercial control sera. They suspended purified enzymes in an albumin solution and stored this solution at -20 °C.…”