Distribution of UDP-glucuronyl transferase among cell fractions of rat liver

Microsomal UDP-glucuronyl transferases (uridine-5′-diphosphate-glucuronate glucuronyl transferase, acceptor unspecific, EC 2.4.1.17) function in detoxification of a wide range of aglycons containing phenolic, alcoholic, carboxylic or amino acceptor groups through formation of water-soluble glucuronic acid derivatives. To localize this activity within a specific cell component, purified rough-surfaced endoplasmic reticulum and Golgi apparatus fractions from rat liver were compared with total homogenates. The UDP-glucuronyl transferase specific activity of the Golgi apparatus fractions was less than or approximately equal to that of the total homogenate whereas this activity was concentrated 3–8 fold in the rough-surfaced endoplasmic reticulum fraction depending upon substrate. We conclude that the rough-surfaced endoplasmic reticulum is the major site of glucuronide formation within the microsome fraction of normal rat livers.     

Comparison of hepatic, renal and intestinal bilirubin UDP-glucuronyl transferase activities in rat microsomes

1. Bilirubin UDP-glucuronyltransferase activity and its dependence on substrate concentrations in rat liver, renal cortex and intestinal mucosa microsomes were studied. 2. Bilirubin monoglucuronide synthesis from unconjugated bilirubin was a higher capacity, lower affinity step in comparison with bilirubin diglucuronide formation in the three tissues tested. 3. Bilirubin glucuronide formation in liver microsomes showed a higher capacity but a lower affinity than extrahepatic ones. Renal cortex and intestinal mucosa exhibited similar kinetics parameters. 4. In vitro bilirubin glucuronidation in renal cortex and intestinal mucosa was quantitatively important as compared with the hepatic one.     

Antioxidant status,lipid peroxidation,mixed function oxidase and UDP-glucuronyl transferase activities in livers from control and DOCA salt-hypertensive male Sprague Dawley rats

The effects of DOCA-salt hypertensive treatment on hepatic glutathione-dependent defense system, antioxidant enzymes, lipid peroxidation, mixed function oxidase and UDP-glucuronyl transferase activities were investigated in male Sprague Dawley rats.Compared with controls, DOCA-salt hypertensive rats had lower body weights (linked to liver hypertrophy). Mixed function oxidase and p-nitrophenol-UGT activities were not affected by the treatment but a significant lower rate of the glucuronoconjugation rate of bilirubin (p < 0.001) was observed in DOCA-salt hypertensive rats. While cytosolic glutathione contents and glutathione reductase activity were not affected, glutathione peroxidase (p < 0.001), glutathione transferase (p < 0.001) and catalase (p < 0.01) activities were decreased and associated with higher malondialdehyde contents (p < 0.001) in treated rats. The imbalance in liver antioxidant status (increasing generation of cellular radical species), associated with increases in lipid peroxidation, suggests that oxidative stress might be directly related to arterial hypertension in DOCA-salt treated male Sprague Dawley rats.     

Tyramine oxidase activity in needle biopsy of normal livers and diseased livers.

Tyramine oxidase and UDP-glucuronyl transferase activities were determined in 52 diseased livers obtained by needle biopsy. 14 liver specimens were also subjected to acetyl CoA carboxylase determination. Tyramine oxidase level was elevated in livers with nonalcoholic fatty change or toxic hepatitis, and reduced in livers with fibrosis or chronic alcoholic injury. UDP-glucuronyl transferase activity was reduced in livers with severe parenchymal damage or hyperbilirubinemia. Acetyl CoA carboxylase activity decreased markedly in an active alcoholic cirrhotic liver, and was elevated in alcoholic fatty livers as well as in a liver with acute venous stasis.     

Prolyl hydroxylase activity in normal and diseased human liver.

Prolyl hydroxylase activity was determined in liver biopsy samples obtained from 10 patients. The liver prolyl hydroxylase values in patients with active hepatitis distribute into two numerical populations based on the extent of elevation over control. The first of these groups includes those with enzyme levels elevated approximately 2.5-fold over normal. Included in this group are patients with active (but nonagrressive) hepatitis and patients where advanced portal fibrosis is already established. The second group where prolyl hydroxylase is elevated approximately nine-fold is comprised of two patients with advanced clinical symptoms of active alcoholic hepatitis with evidence of aggressive cirrhosis but with only early minimal evidence of existing fibrosis.     

ADP-ribosyl transferase and NAD glycohydrolase activities in rat liver mitochondria

ADP-ribosyl transferase and NAD glycohydrolase activities have been estimated in mitochondria in mitoplasts as well as in other submitochondrial fractions. A high activity of these two enzymes was present in mitoplasts as compared to the outer membrane preparation or intermembrane compartment. Inhibitor studies provide strong evidence for the involvement of ADP-ribosyl transferase in the process of ADP-ribosylation of mitochondrial proteins. When NAD glycohydrolase was blocked by nicotinamide or 3-aminobenzamide, the incorporation of ADP-ribose into mitochondrial proteins still occurs. ADP-ribosyl transferase activity could also be detected when NAD glycohydrolase was separated by hydroxylapatite chromatography. The protein-linked ADP-ribose moiety appears to be an oligomer in mitochondria.     

Bile pigments and bilirubin UDP-glucuronyl transferase during the metamorphosis of Rana catesbeiana tadpoles

1. Cold-acclimated (1 degree C) goldfish (Carassius auratus) branchial Na/K-ATPase activity was elevated 100% while renal Na/K-ATPase activity was not significantly affected compared with warm-acclimated (20 degrees C) goldfish. 2. Cold-acclimated goldfish branchial and renal Mg-ATPase activity was reduced 18 and 30% on a per mg protein basis, respectively. 3. Renal Na/K-ATPase activity was 4.6- and 1.6-fold greater than gill in cold- and warm-acclimated fish, respectively. 4. The elevated branchial Na/K-ATPase activity and the unchanged renal Na/K-ATPase activity are consistent with the maintenance of the reduced blood ion level in cold-acclimated goldfish.     

Steroid sulfatase and sulfuryl transferase activities in human brain tumors

Neuroactive steroids (dehydroepiandrosterone, pregnenolone) and their sulfates act as modulators of glutamate and γ-aminobutyrate type A receptors in the brain The physiological ratio of these neuromodulators is maintained by two enzymes present in the brain, namely, steroid sulfatase (STS) and steroid sulfuryl transferase (SULT).

Following previous determination of their activities in monkey brains, their activities were evaluated in human brain tumors. Radioimmunoassay and GC-MS were used for determination of products. Both enzyme activities were measured in the 55 most frequent human brain tumors (glioblastomas, pituitary adenomas, meningiomas, astrocytomas).

Significant differences were found in STS activity among investigated types of tumors except the pair of pituitary adenomas-glioblastomas, while significant differences were found in SULT activity among investigated types of tumors.

Spontaneous tendency to form clusters was revealed when both enzyme activities were taken as coordinates. Clustering indicated an individual metabolic behavior of glioblastomas and 72.7% of pituitary adenomas. Astrocytomas, meningiomas and remaining 27.3% pituitary adenomas showed similarities in both enzymes’ activities. Differences in STS and SULT activity did not depend on the sex or age of subjects.     

Bilirubin UDP-glucuronyltransferase activity in human fetal liver homogenates]

The bilirubin UDP GT-activity of the liver was studied from week 15 of pregnancy in 23 human fetuses and mature and immature dead newborns, respectively. No measurable bilirubin UDP GT-activity was found up to week 26 of pregnancy. The development of enzymatic activity presumably starts only postnatally, irrespective of gestational age of birth weight. Up to the fifth day the bilirubin UDP GT-activity is less than 0.2 mg of conjugated bilirubin/g liver/h, reaching in the second week values that correspond to approximately 20--30% of adult values. This activity is sufficient to prevent a clinically important hyperbilirubinemia because the concentration of unconjugated serum bilirubin was in all children below 12mg/100 ml.     

Sialyl transferase activities of rat ascites hepatoma cells and rat liver

Sialyl transferase activities of the homogenate of rat ascites hepatome cells were compared with normal rat liver homogenate. The former had only 20% of the activity of the latter when an exogenous acceptor was added in the reaction mixture.Toward endogenous receptors, the activity of the hepatoma cell homogenate was 50% of that of the normal cell homogenate. A stimulation of the activity toward endogenous acceptors was observed when the homogenate of rat ascites hepatoma cells and that of rat liver were mixed. This stimulatory effect seems to be the consequence of utilization of acceptors from ascites hepatoma cells by the sialyl transferases of the rat liver.     

Cell surface glycosyl transferase activities in liver cells of developing chicken embryos

Summary The cell surface of embryonic chick liver cells contains transferases for mannose, fucose, galactose, N-acetyl-glucosamine and N-acetyl-neuraminic acid. Liver cells obtained by trypsin-dissociation of the tissue use the corresponding exogenous sugar nucleotides as substrates. The activities of the enzymes tested do not depend neither on the dissociation procedure nor onde novo protcin synthesis. They vary considerably during development of the embryos, reaching maximal values at the 8th ± 1 day and at the 12th ± 1 day. Glycoproteins are the final stable endogenous acceptors for all sugars. Mannose transfer proceeds via a two or multistep reaction sequence. In a first step labile lipophilic intermediates are formed. Mannose can be liberated by treating the intermediates with 0.1n HCI at 100°C. In a second reaction step mannose becomes attached to glycoproteins. From embryonic chick liver cells a glycopeptide fraction has been obtained by pronase digestion followed by several purification steps. The purified glycopeptides inhibit all transferase systems and act as exogenous acceptors for mannose transfered from exogenous GDP-mannose.     

Influence of temperature on the determination of enzyme activities in human serum. gamma-Glutamyl transferase.

Optimum reaction conditions for determination of gamma-glutamyl transferase were studied at 25, 30 and 37 degrees C using a kinetic test and gamma-glutamyl-3-carboxy-4-nitranilide as substrate. There was no dependence on temperature of half saturation constants of gamma-glutamyl-3-carboxy-4-nitranilide. The corresponding constants for glycylglycine were influenced by temperature and the pH. The optimum showed a dependence upon temperature. In Arrhenius' plot, a deviation from straight line can be observed only above 35 degrees C. The influence of temperature on the determination of enzyme activities in human serum are discussed.     

Development of multiple activities of UDP-glucuronyltransferase in human liver.

UDP-glucuronyltransferase activities towards eight substrates were assayed in samples of foetal, term and adult human liver. Activities towards bilirubin, androsterone, testosterone, 1-naphthol, 4-nitrophenol and 2-aminophenol were present in foetal and term liver samples at less than 14% of adult values, whereas activity towards 5-hydroxytryptamine was present in foetal and term liver at 109 and 121% of adult values respectively. Thus a 'foetal' form of UDP-glucuronyltransferase may exist in human liver that is more restricted in substrate specificity than are those of the rat or rhesus monkey.