Spectrophotometric measurement of aspartate aminotransferase activity in mammalian and fish semen

The Karmen assay (Karmen, A., 1955. J. Clin. Invest., 34: 131–133) of aminotransferase activity as modified by the International Federation of Clinical Chemistry (Bergmeyer, H.U., Horder, M and Rej, R., 1986. J. Clin. Chem. Clin. Biochem., 24: 497–510) appeared to be useful for semen analysis, after a few additional modifications. The assay system does not work for neat bull seminal plasma; however, enzyme activity can be measured correctly in diluted samples. In many cases, slight inhibition of enzyme activity was observed at 240 mM of l-aspartate. For this reason, a lower concentration of this substrate should be used. The higher sensitivity of this modified Karmen method offers more accurate measurement of aspartate aminotransferase activity in semen as compared with the methods employed previously.