A METHOD FOR THE DETECTION OF ATYPICAL FORMS OF HUMAN SERUM CHOLINESTERASE. DETERMINATION OF DIBUCAINE NUMBERS

Abstract

Cases with atypical esterase activity were found by determining esterase inhibition in numerous sera. A suitable inhibitor was the local anaesthetic dibucaine (cinchocaine, TN Nupercaine, Perkain). A good discrimination between typical and atypical sera was obtained under the following conditions: The esterase activity of human serum diluted 1:100 was measured with a recording spectrophotometer at 240 mμ. The substrate was 5 × 10−5 M benzoylcholine dissolved in M/15 phosphate buffer, pH 7.4. The concentration of the inhibitor was 10−5 M. With the experimental temperature around 25 °C, the average inhibition of the typical enzyme was 78.8 ± 0.3%. The inhibition of the atypical esterases was less; in rare cases the inhibition was only 16%. For each person, the inhibition characteristics were constant over a period of several months, and independent of the esterase level. The degree of inhibition measured under these conditions and expressed in per cent has been termed "Dibucaine Number".