Liver enzyme, activation process

Liver cancer can be induced in rats by localized irradiation (UNSCEAR, 1977) or by a number of different chemicals and dosage schedules (Farber, 1984). Initiation-promotion protocols are also effective inducers of liver tumors. The predominant lesions are preneoplastic nodules, but as in the skin, carcinomas arise late in the process. Altered hepatic cell fod can be identified within a few weeks after the start of carcinogen treatment by specific changes in enzyme activity, inability... 

Nordlie and Lygre (118, 132) have carried out detailed pH kinetic studies of PPi-glucose phosphotransferase, CDP-glucose phosphotransferase, and glucose-6-P phosphohydrolase activities with partially purified rat liver enzyme preparations, and they have concluded, on the basis of sharp, unit-changes in slopes of Dixon (133) plots of pKm for phosphate substrates vs. pH near 6.5, that enzyme-bound histidine may participate directly in the catalytic process. Values of Km for glucose were unaffected by reaction mixture pH Km values and relative Vmax values calculated for infinite concentrations of all substrates are tabulated in Table IX. 

In addition, PolyPs are most likely involved in the regulation of enzyme activities by participation in their phosphorylation. A protein phosphorylation process, using not ATP but high-polymer PolyPs, was revealed in the archae Sulfolobus acidocaldarius (Skorko, 1989). Tripolyphosphate was observed to be a phosphodonor of selective protein phosphorylation of rat liver microsomal membrane (Tsutsui, 1986). 

The relation between tissue injury and the appearance of enzymes in the circulation is most clearly seen in the condition of myocardial infarction, in which a relatively short episode of damage is followed by a rapid transfer of enzymes to the circulatory system. About 24 hours after a myocardial infarction, the pattern of relative activity of various enzymes in the circulatory system closely resembles that in the myocardial tissue. These relationships are less clearly recognized in other conditions, such as chronic liver disease, in which enzyme release is a process that continues for a period of time. The pattern of relative enzyme activities in serum in chronic disease may also become distorted by differential rates of removal of enzymes from the circulation and possibly also by differential changes of rates of enzyme synthesis in the affected tissue. 

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