The development and evaluation of a homogeneous immunoassay for the isoenzymes of aspartate aminotransferase

A homogeneous assay system of aspartate aminotransferase iso-enzymes using proteases and application for clinical evaluation of myocardial infarction

We designed a rapid, homogeneous assay for human aspartate aminotransferase (AST) isoenzymes, by a selective proteolysis of soluble AST (s-AST), using chymotrypsin and protease 401. The linearity of mitochondrial (m-AST) was elongated up to 4000 U/l. m-AST values from the human liver, and determined by a homogeneous assay using protease 401 or chymotrypsin, were relative to those obtained using an immunoprecipitation method. In perioperative patients or those with an acute myocardial infarction, the peaks of s-AST and m-AST values were noted 13 h and at 57 h after ictus, respectively, whereas the peak of ratio between was seen 6 h after ictus. In the case of Budd-Chiari syndrome, the maximum levels of the two AST activities were evident 14 days after hospitalization and the peak of ratio between them was seen after 7 days. We propose that this homogeneous assay can serve as a diagnostic tool for early phase detection of myocardial infarction and of Budd-Chiari syndrome.

An avidin-biotin ELISA for the measurement of mitochondrial aspartate aminotransferase in human serum

We describe a new double-antibody ELISA system using avidin-biotin amplication for the mass measurement of mitochondrial aspartate aminotransferase (m-AST) in human serum. The assay is very sensitive and as little as 0.5 ng/ml of m-AST may be detected. The method is linear up to 100 micrograms/l. The within-day and day-to-day coefficients of variation were found to be 8.9% and 11.5% respectively for a low m-AST concentration (2.7 micrograms/l), and 5.9% and 8.0% respectively for a high level of m-AST (30 micrograms/l). The assay requires 100 microliters of serum and can be completed within 5 h. The ELISA procedure and a classical immunoprecipitation technique measuring the catalytic activity of the isoenzyme were applied simultaneously to the sera of 189 subjects. The protein levels determined by ELISA correlated poorly (r = 0.66) with the catalytic activity of m-AST.

Measurement of aminotransferases: Part 1. Aspartate aminotransferase

Aminotransferases are ubiquitous enzymes of mammalian cells and several are of important diagnostic use. The application of aspartate aminotransferase activity measurements in serum from individuals suffering from myocardial infarction brought about a new dimension in clinical laboratory testing in the 1950s. This review focuses on measurement techniques for aspartate aminotransferase and their application (a subsequent article will review other aminotransferases). Assay techniques measuring enzyme activity are direct spectrophotometric measurements, manometric techniques, assays using dye substances, coupled enzyme techniques, and radiometric procedures. Of these procedures, the one employing malate dehydrogenase and NADH is the most important and is covered in particular detail. The estimation of the mitochondrial isoenzyme of aspartate aminotransferase is also of clinical interest, in particular for estimating severity of disease or in specific applications (e.g., chronic alcoholism). Methods reviewed for estimation of this enzyme are electrophoresis, chromatography, differential kinetic behavior, and immunochemical separation. Determination of the enzyme protein by techniques independent of its catalytic activity are also reviewed.