Development of alcohol dehydrogenase activity in the human liver.

Abstract

Extract: In the present study, alcohol dehydrogenase activity (ADH) has been measured in human liver tissue during development, and a comparison made between certain kinetic properties of crude enzyme preparations from fetal and adult liver. The fetal livers were obtained from legal abortions. The liver tissue from children and adults was acquired during surgery of the abdomen in cases where no macroscopic abnormality of the livers was observable. The liver tissue was frozen immediately after excision. Studies indicated that the enzyme activity was stable at −20° for up to 6 days. All the determinations were made within 24 hours of the liver being sampled. A 10% liver homogenate was prepared in ice-cold 0.25 M sucrose containing 1 % Triton X-100. After centrifugation of the homogenate for 10 minutes at 5000 × g at 3°C, samples were taken from the supernatant for protein determination and for enzyme assays. Table I presents the enzyme activity levels in human liver during the development from a fetus to an adult organism. The results are expressed as milliunits per g liver wet weight and per 100 mg soluble liver protein. ADH activity is detectable in 2-month-old fetuses, although it amounts to no more than 3–4: % of adult activity. Activities of adult range are found after 5 years of age. Considerable varation exists in the activity of adult livers. The relationship between pH and the rate of reaction appears in figure 1. The final pH figures of the reaction mixtures are given; these were determined with a Radiometer pH meter. Adult human liver ADH has a pH optimum of about 10.4, and the pH optimum for the fetal enzyme preparations is 10.0. Lineweaver-Burk analyses which illustrate the relationship between the concentration of ethanol and NAD, and the ADH activity in adult and fetal liver are presented in figures 2 and 3. The results presented are typical of three cases studied in each group. Close agreement was found for all constants in the different enzyme preparations examined. The apparent Km values for ethanol were 3400 μM. and 1100 μM, and for NAD 70 μM and 150 μM in fetal and adult enzyme preparations respectively. Speculation: These results do not constitute a foundation for a conclusion whether the fetal and the adult enzyme preparations are composed of a similar isoenzyme pattern. Studies which make use of purified enzyme and isoenzyme preparations are needed. Nevertheless, the results presented here suggest that variants may be found in alcohol dehydrogenase during development.