The level of gamma-glutamyltransferase in serum, effect of carbohydrate heterogeneity on clearance rate.

The measurement of serum gamma-glutamyltransferase (GT) is a frequently used parameter of liver diseases. The serum enzyme originates from liver and is cleared from the circulation by the galactose receptor in liver. The rate of uptake will thus vary with the amount of terminal galactose residues on the enzymes' carbohydrate moiety. Using an experimental rat model we have studied the relative clearance rates of variant forms of GT with different carbohydrate composition. GT purified from pancreas and kidney contains less sialic acid and showed considerably higher clearance rates than the enzyme from liver. The rapid uptake of the kidney and pancreas enzymes indicates that these enzymes may not reach detectable levels if released from these organs to the circulation. On the other hand, GT in serum of alcoholics contains increased amount of sialic acid and this enzyme variant showed a slightly decreased clearance rate compared to the normal liver enzyme. Increased sialylation of GT may thus contribute to the increased level of the enzyme in serum after alcohol abuse.