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At least 19 recordsLinked to original sources
PubMed1993

Cloning and characterization of a cDNA encoding chicken liver alpha-N-acetylgalactosaminidase.

Chicken liver alpha-N-acetylgalactosaminidase (alpha AGA) specifically removes terminally alpha-linked alpha-N-acetylgalactosamine from oligosaccharide chains on the surface of group A erythrocytes. Here, we report the molecular cloning of a alpha AGA cDNA by both library screening and PCR amplification. The clone contains a 1.2-kb 3'-untranslated region and 1.2-kb coding region which encodes a 45-kDa protein. The protein was produced in bacteria and in rabbit reticulocyte lysate, and is specifically recognized on Western blot by an antibody raised against the purified chicken liver enzyme. Enzymatic activity was detected when alpha AGA was produced in Saccharomyces cerevisiae. The deduced amino acid sequence shows 80% homology with human alpha AGA and about 60% homology with alpha-galactosidases from a number of sources, indicating that these two families of exoglycosidases are evolutionarily related.

Amino Acid Sequence↗
PubMed1988

Possible involvement of histidine residues in the loss of enzymatic activity of rat liver malic enzyme during aging.

During aging there is a decrease in activity of the malic enzyme in rat liver. The "old" malic enzyme is about 36% less active than the "young" enzyme. Some properties and modifications of amino acid residues are studied here (--SH, arginine, methionine, histidine, lysine) to try and check on the existence of any relationship between them and the loss of enzymatic activity during aging. Diethyl pyrocarbonate measurements indicate that the old enzyme has 1 histidine residue less than the young enzyme. Moreover, the treatment of the young enzyme with ascorbate for 15 min produces the loss of 36% of the enzymatic activity and the loss of 1.2 histidine residues. These results suggest that during aging the modification of the histidine residue could be involved in the loss of its enzymatic activity.

Aging↗
PubMed1992

Cooperative binding is not required for activation of muscle phosphorylase.

Muscle and liver glycogen phosphorylase isozymes differ in their responsiveness to the activating ligand AMP. The muscle enzyme, which supplies glucose in response to strenuous activity, binds AMP cooperatively, and its enzymatic activity becomes greatly enhanced. The liver isozyme regulates the level of blood glucose, and AMP is not the primary activator. In muscle glycogen phosphorylase, the residue proline 48 links two secondary structural elements that bind AMP. This amino acid residue is replaced with a threonine in the liver isozyme; unlike the muscle enzyme, liver binds AMP noncooperatively, and the enzymatic activity is not greatly increased. We have substituted proline 48 in the muscle enzyme with threonine, alanine, and glycine and characterized the recombinant enzymes kinetically and structurally to determine if proline at this position is critical for cooperative AMP binding and activation. Importantly, all of the engineered enzymes were fully activated by phosphorylation, indicating that enzymatic activity was not compromised. Only the mutant enzyme with alanine at position 48 responds like the wild-type enzyme to the presence of AMP, indicating that proline is not absolutely required for full cooperative activation. The substitution of either threonine or glycine at this position, however, creates enzymes that no longer bind AMP cooperatively. The enzyme with threonine at position 48 further mimics the liver enzyme, in that the maximal enzymatic activity is also reduced. Significantly, the glycine substitution caused the enzyme to be fully activated by AMP, although binding was not cooperative. The hyperactivation of the glycine mutant by AMP suggests that the total free energy of activation has decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Monophosphate↗
PubMed1986

Quantitation of glycogen synthase and phosphorylase protein in mouse liver: correlation between enzymatic protein and enzyme activity.

Phosphorylase and glycogen synthase protein were measured in normal and genetically diabetic (C57BL/KsJ db/db) mice liver extracts using rocket immunoelectrophoresis, and these data correlated with measurements of total phosphorylase and total glycogen synthase activities, respectively. Phosphorylase protein in 5-week-old normal mice was about 5 micrograms/mg protein and reached 8 micrograms/mg protein by 9 weeks. In comparison, the diabetic mice had elevated levels of phosphorylase protein (11-13 micrograms/mg protein) which correlated with an increased total phosphorylase activity compared to normals. The correlation coefficient for the phosphorylase activity vs protein plot was highly significant (r = 0.73, P less than 0.001). The molar concentration of phosphorylase subunit in normal mouse liver was calculated to be 11 microM and up to 23 microM in the diabetic mice. The liver concentration of glycogen synthase was relatively constant in normal mice at 400 ng/mg protein (corresponding to approximately 1.4 microM) but varied from 230 to 441 ng/mg protein (0.9 to 1.8 microM) in diabetic mice. There was little correlation between glycogen synthase activity and enzymatic protein (r = 0.15). These results indicate (1) that phosphorylase is present at concentrations approximately 10 times that of glycogen synthase, and (2) that glycogen synthase activity is relatively more dependent upon factors other than the amount of enzymatic protein.

Animals↗
PubMed1992

Characterization of the tetramer-dimer-monomer equilibrium of the enzymatically active subunits of pigeon liver malic enzyme.

The tetrameric malic enzyme from pigeon liver was reversibly dissociated in the sequence of tetramer-dimer-monomer in an acidic environment (pH 4.5) or when the ionic strength or temperature of the solution was perturbed (0.2 M ammonium sulfate or < 10 degrees C). The dissociated monomer was enzymatically active according to the following criteria: (a) separation and direct activity staining of the monomer in the native gradient polyacrylamide gel, (b) activity staining of the monomer at its pI region in the isoelectric focusing gel, and (c) the enzyme showing lower but definite enzyme activity under conditions where only monomer existed in the solution. The catalytic constant (kcat) and specificity constant (kcat/KmMal) for the monomer were found to be 19 +/- 6 s-1 and 58 x 10(3) s-1.M-1, respectively, only one-seventh and one-seventeenth of those for the tetramer. Different types of interactions are involved in the monomer-monomer and dimer-dimer associations: (a) Two dissociation processes showed different pH dependences. The monomer-monomer interactions involve an amino acid with a side chain pKa value around 5.7, and an amino acid with a side chain pKa value of 7.2 is involved in the dimer-dimer association. (b) Ammonium sulfate up to 0.2 M only affects the monomer-monomer but not the dimer-dimer interactions. The Gibb's free energy, enthalpy, and entropy all have negative values for the above subunits' dissociations. The overall dissociation is an enthalpy-driven process. Association of the subunits to form dimers and tetramers involves salt-bridge, van der Waals, and hydrogen-bonding interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[The effect of plant aromatic substances on the activity of various enzymes in the rat blood and liver].

Enzymatic activity was studied in blood plasma, erythrocytes and liver tissue homogenate of rats treated with vegetable aromatic substances. 60 rats were kept within 3 months in atmosphere containing naturally occurring concentrations of monarde ester oil. Control animals were maintained in usual atmosphere of vivarium. In liver tissues of control animals glycolytic processes predominated as shown by the data on increased activities of lactate- and glucose-6-phosphate dehydrogenases. At the same time, activity of soluble microsomal enzyme acetyl esterase was decreased in liver tissue, while activity of these esterases was increased in blood plasma, thus suggesting that membrane structures were destabilized. Aromatic fractions of monarde ester oil, introduced into atmosphere, contributed to normalization of the enzymatic reactions studied.

Acetylesterase↗
PubMed1991

Relationship between growth and selected liver enzyme activities of individual rainbow trout.

Interpretation of enzymatic data requires consideration of the food intake of each animal studied. Food intake and body mass gain are closely correlated in rapidly growing animals. Direct measurement of food intake by individual fish within a school is nearly impossible. We examined the relationship between growth and liver enzyme activity as a means of inferring the food intake of individual fish within a school. Trout, identified by passive integrated transponder implants, were fed either 0, 0.3, 1, or 2% body mass/d to produce a wide range of growth rates. The activities of five enzymes, predominantly localized in liver, were measured. Results showed that, although the magnitude of response differed, increases in total liver activities of all five enzymes measured were linearly related to growth. Hexokinase (EC 2.7.1.1) increased at a rate below, and beta-D-glucose:NAD(P)+1-oxidoreductase (EC 1.1.1.47) increased at a rate equivalent to, observed increases in total liver mass. Malic enzyme (EC 1.1.1.40), glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44) showed preferential increases in activity as food intake increased. Correlation of enzyme activities measured in fish fed restricted rations with either growth or nominal feeding rate showed that growth of individual fish was more closely related to liver enzyme activities than nominal feeding rate.

Animals↗
PubMed1996

Regulation of gene expression and activity of malic enzyme in liver of hereditary hypertriglyceridemic (hHTG) insulin resistant rat: effect of dietary sucrose and marine fish oil.

The effect of increased dietary intake of n-3 polyunsaturated fatty acids (PUFA) on hepatic malic enzyme (EC 1.1.1.40) gene expression and activity was investigated in either hereditary fixed or dietary induced hypertriglyceridemia after euglycemic hyperinsulinemic (6.4 mU/kg/min) clamp. The hereditary hypertriglyceridemic rats (hHTG) were fed for 2 weeks basal (B) or high (63 cal %) sucrose (HS) diet, with or without fish oil (FO, 30 wt % n-3 PUFA). The results were compared with the data obtained in control (C) animals subjected to identical protocol. In hHTG rats, increased gene expression [hHTG: 1.7 +/- 0.1 vs. C: 0.5 +/- 0.05 arbitrary units (AU), P<0.02] for malic enzyme (ME) was not accompanied by increased activity of this enzyme in liver [hHTG: 1.1 +/- 0.1 vs. C: 3.1 +/- 0.4 nkat/mg, P<0.001]. HS feeding raised the activity [HS-hHTG: 4.2 +/- 0.3 nkat/mg, P<0.001; HS-C: 7.5 +/- 0.9 nkat/mg, P<0.001] and mRNA levels [HS-hHTG: 10.4 +/- 0.3 AU, P<0.001; HS-C: 7.7 +/- 0.3 AU, P<0.001] in liver of both hHTG and control rats. The supplementation of HS diet with FO led to striking suppression of activity by 63 % [2.8 +/- 0.5 nkat/mg, P<0.001] and gene expression [2.9 +/- 0.2 AU, P<0.001] for ME in liver of control rats. Such inhibitory effect was not as pronounced in hHTG rats and reached about 50 % in the ME activity [HS+FO: 2.0 +/- 0.06 nkat/mg vs. HS:4.2 +/- 0.3 nkat/mg, P<0.001] or 30 % decrease in ME mRNA levels [HS+FO: 7.5 +/- 0.8 Au vs. HS:10.4 +/- 0.3 AU, P<0.001]. Thus, hHTG rats have markedly elevated levels of mRNA for malic enzyme in liver accompanied by decreased enzymatic activity. Dietary manipulations leading to alteration of hypertriglyceridemia (HS diet, omega-3 PUFA) influenced both the activity of malic enzyme and its transcription in the liver.

Journal Article↗
PubMedDate not supplied

Conversion of retinoid ethers to alcohols by enzymatic activity present in rat liver microsomes.

An enzyme present in rat liver microsomes catalyzes the conversion of retinyl methyl ether (RME) to retinol; NADPH is required for activity. The optimum pH for the reaction is 7.4; the KM and Vmax values are 120 microM RME and 14.3 nmol of retinol/mg protein/hr, respectively. As a substrate, the 2,3,6-trimethyl-4-methoxyphenyl analog of RME is as effective as RME. There is, however, no measurable activity for dealkylation of retinyl ethyl ether or retinyl butyl ether. Hepatic enzyme activity for the metabolism of RME is induced by 3-methylcholanthrene but not by phenobarbital or RME itself. The induced activity also requires NADPH as a cofactor. The optimum pH for the induced enzyme is 8.4; the KM and Vmax values are 50 microM RME and 111 nmol of retinol/mg protein/hr, respectively. For this enzyme, RME is a better substrate than the 2,3,6-trimethyl-4-methoxyphenyl analog of RME; retinyl ethyl ether is less effective; and again, there is no measurable activity with retinyl butyl ether as a substrate. Neither constitutive nor induced activity is detectable in microsomes from lung, spleen, stomach, kidney, small intestine, or large intestine. The enzyme activity that cleaves retinoid ethers appears to be similar to other microsomal NADPH-requiring O-dealkylases and different from a reported tetrahydropteridine-requiring dealkylase.

Alcohols↗
PubMed1987

Glycerol phosphorylation and oxidation in pancreatic islets.

Homogenates of rat pancreatic islets and tumoral islet cells (RINm5F line) were found to display glycerokinase activity. In the islets like in the liver, about one-sixth of the enzyme appears bound to mitochondria. The enzymatic activities in liver and islets differ from one another, however, by their response to increasing concentrations of either glycerol or ATP and sensitivity to inhibition by D-glyceraldehyde. In intact islets, [U-14C]glycerol is efficiently oxidized, albeit at a much lower rate than that found for its phosphorylation by islet homogenates. These findings are relevant to the role played by glycerol liberated from endogenous triglycerides in the basal respiration of islet cells.

Adenoma, Islet Cell↗