Development of radioimmunoassay for gamma-glutamyl transferase using pancreatic enzyme

Kinetic study of gamma-glutamyltransferase activity by electrophoretically mediated microanalysis combined with micellar electrokinetic capillary chromatography

The use of capillary electrophoresis for the determination of gamma-glutamyltransferase (GGT) activity with gamma-glutamyl-p-nitroanilide (Glu-p-NA) as a substrate was investigated. The reaction velocity was quantified spectrophotometrically by the corrected peak area of the product p-nitroaniline (pNA) at 380 nm. Micelles composed of sodium deoxycholic acid were used in the background electrolyte in order to obtain a baseline separation between the substrate and the product. The presence of the micelles did not influence the enzymatic reaction. The electrophoretic system was used, not only for the separation and quantitation of the different reaction compounds but also for the in-capillary mixing of the enzyme and substrate plugs. This methodology is known as electrophoretically mediated microanalysis (EMMA). With the developed in-capillary activity assay an average Michaelis constant (K(M)) for GGT was calculated to be 2.09 mM (RSD = 7.3%, n = 3), a value consistent with previously reported values.

Gamma glutamyl transferase

Serum gamma-glutamyl transferase (GGT) has been widely used as an index of liver dysfunction and marker of alcohol intake. The last few years have seen improvements in these areas and advances in understanding of its physiological role in counteracting oxidative stress by breaking down extracellular glutathione and making its component amino acids available to the cells. Conditions that increase serum GGT, such as obstructive liver disease, high alcohol consumption, and use of enzyme-inducing drugs, lead to increased free radical production and the threat of glutathione depletion. However, the products of the GGT reaction may themselves lead to increased free radical production, particularly in the presence of iron. There have also been important advances in the definition of the associations between serum GGT and risk of coronary heart disease, Type 2 diabetes, and stroke. People with high serum GGT have higher mortality, partly because of the association between GGT and other risk factors and partly because GGT is an independent predictor of risk. This review aims to summarize the knowledge about GGT's clinical applications, to present information on its physiological roles, consider the results of epidemiological studies, and assess how far these separate areas can be combined into an integrated view.

The sugar-chain heterogeneity of human gamma-glutamyl transferases from the reproductive system and kidney

The sugar-chain heterogeneity of gamma-glutamyl transferase (gamma-GTP, EC 2.3.2.2) from the human reproductive system (seminal plasma, prostate and testis) and kidney was investigated using the serial lectin affinity technique and their properties were compared. According to the results of serial lectin affinity chromatography, a possible sugar chains of enzymes from reproductive system were mainly of the hybrid type without fucose linkages to the innermost GlcNAc and/or the biantennary complex type sugar chains and a few were of the multiantennary complex-type with branched GlcNAc (beta 1-4) Man and bisecting complex type sugar chains. On the contrary, the major sugar chains of kidney gamma-GTP were of the multiantennary complex type and/or bisecting complex type sugar chains. Results of isoelectric focusing showed the gamma-GTP bound multiantennary complex type sugar chains to be the most acidic glycoprotein. Moreover, the biantennary type sugar chains were slightly more acidic than the high mannose and/or hybrid type sugar chains, varying with the degree of sialylation.

Monoclonal antibodies to human kidney gamma-glutamyltransferase

Eight hybridoma clones secreting large amounts of monoclonal antibodies against purified human kidney gamma-glutamyltransferase (GGT) were isolated and produced in ascites. None of them inhibits the catalytic activity of GGT. They all bind to the heavy subunit of this dimeric enzyme. Immunoblot analysis showed that these antibodies react with the catalytically active GGT. The monoclonal antibodies also recognize the heavy subunit of the human liver enzyme. This is of interest, as serum GGT is known to originate from the liver. None of the monoclonals reacts with GGTs from rat or pig kidney. After identification of epitopes specificities, the antibodies will be used for the development of immunoassays of GGT especially in human serum.

Measurement of activation energy of gamma-glutamyltransferase as a marker for enzyme heterogeneity

In order to detect differences between various multiple forms of gamma-glutamyltransferase, the activation energy was measured. In the serum of patients with liver diseases, activation energy was measured. In the serum of patients with liver diseases, activation energy of the serum enzyme is higher than in normal individuals (41.9 +/- 1.2 vs. 38.9 +/- 1.5 kJ/mol, p less than 0.05). Neuraminidase treatment resulted in a reduction of activation energy. Various multiple forms of serum gamma-glutamyltransferase, as prepared by lectin affinity chromatography (concanavalin A, Ricinus communis I and II, wheat germ agglutinin) showed activation energy differences between binding and nonbinding fractions. Similar results were observed in seminal plasma gamma-glutamyltransferase, when patients with accessory gland infection were compared with a reference population. Our results suggest that the activation energy depends upon differences in the carbohydrate part of the enzyme. The low gamma-glutamyltransferase activation energy of tissue extracts increased significantly after butanol extraction and was then comparable with serum activation energy values, which suggests that lipid-binding is a factor in activation energy variation. In most cases, gamma-glutamyltransferase activities measured at a certain temperature can be easily converted to a corresponding activity at another temperature, but in severe liver disease significant errors may be introduced when simple temperature conversion factors are used.

Variations in sialic acid content of gamma-glutamyltransferase: a consequence for immunochemical determinations?

Using specific antibodies against the human kidney enzyme, gamma-glutamyltransferase (GGT, EC 2.3.2.2) was assayed from human kidney and serum by electroimmunodiffusion. Determination of the enzyme by such a method was highly influenced by the sialic acid content of the molecule. The peaks corresponding to the sialylated GGT were higher than those corresponding to the neuraminidase-treated enzyme. In contrast, sialylation of the protein had no influence on the results observed when measuring the enzyme by radial immunodiffusion. Moreover, immunoprecipitation curves of both sialylated and neuraminidase-treated samples were identical. The varying degrees of sialylation of GGT occurring under physiological or pathological conditions are known to be partly responsible for the heterogeneity of the enzyme in organs and biological fluids. Therefore, determination of the enzyme by electroimmunodiffusion may be hazardous.