THE LEVEL OF GAMMA-GLUTAMYL-TRANSFERASE IN SERUM, EFFECT OF CARBOHYDRATE HETEROGENEITY ON CLEARANCE RATE

The measurement of serum gamma-glutamyltransferase (GT) is a frequentl y used parameter of liver diseases. The serum enzyme originates from l iver and is cleared from the circulation by the galactose receptor in liver. The rate of uptake will thus vary with the amount of terminal g alactose residues on the enzymes' carbohydrate moiety. Using an experi mental rat model we have studied the relative clearance rates of varia nt forms of GT with different carbohydrate composition. GT purified fr om pancreas and kidney contains less sialic acid and showed considerab ly higher clearance rates than the enzyme from liver. The rapid uptake of the kidney and pancreas enzymes indicates that these enzymes may n ot reach detectable levels if released from these organs to the circul ation. On the other hand, GT in serum of alcoholics contains increased amount of sialic acid and this enzyme variant showed a slightly decre ased clearance rate compared to the normal liver enzyme. Increased sia lylation of GT may thus contribute to the increased level of the enzym e in serum after alcohol abuse.