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Clinical Chemistry 21: 1277-1281, 1975;
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Clinical Chemistry, Vol 21, 1277-1281, Copyright © 1975 by the American Association for Clinical Chemistry

New Instrument for Rapid Determination of Activities of Lactate Dehydrogenase Isoenzymes

Johannes Everse 1, Richard M. Reich 2, Nathan O. Kaplan 3, and W. Donald Finn 2

1 Department of Chemistry, University of California-San Diego, La Jolla, Calif. 92037
2 American Instrument Co., Silver Spring, Md. 20910.
3 Department of Chemistry, University of California-San Diego, La Jolla, Calif. 92037Department of Chemistry, 4080 Basic Science Building, University of California-San Diego, La Jolla, Calif. 92037.

Lactate dehydrogenase isoenzymes can be distinguished kinetically by the fact that isoenzyme H is strongly inhibited a few seconds after the reaction is started if high concentrations of pyruvate are present, in contrast to the M isoenzyme. A new instrument that exploits this fact can measure both the total activity and the proportion of H isoenzyme in serum or plasma in 8 to 10 s. The instrument consists of a simplified stoppedflow apparatus in which the plasma is assayed for lactate dehydrogenase activity, and an electronic device that measures the rate of the reaction at two pre-set time intervals. The first rate is taken between 0.2 and 0.4 s after the reaction is started, a time at which both isoenzymes are fully active, and at which the rate obtained thus reflects total lactate dehydrogenase activity in the plasma sample. The second rate is measured 4 to 6 s after the start of the reaction, at which time the H isoenzyme has become inhibited and the observed rate compared to the initial rate is therefore proportional to the percentage of H isoenzyme activity in the serum. These two rates are electronically displayed on two three-digit voltmeters, the first display being the total activity, the second a number proportional to the inhibited slope. The percentage of M isoenzyme can then be calculated from the initial and final rate. A total of five to six repeat assays may be done within a minute on 1 ml of plasma or serum. This instrument may be of significant value in following the progress of myocardial infarctions and other diseases.


Key Words: heart disease • following enzyme activity with time • analytical systems

Submitted on May 5, 1975
Accepted on May 31, 1975






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Copyright © 1975 by the American Association for Clinical Chemistry.