Immunofluorescent and histochemical localization of AMP deaminase in skeletal muscle.

Fluorescent antibody staining experiments with both isolated myofibrils and muscle fibers grown in culture show that AMP deaminase is bound to the myofibril in the A band. The strongest staining occurs at each end of the A band. The approximate width of the fluorescent stripes and their relation to the A band remains constant as a function of sarcomere length. Removal of enzyme from the myofibrils leads to loss of staining, and readdition of purified enzyme restores the original staining pattern. A histoenzymatic method for the detection of AMP deaminase activity in cultured fibers gives comparable localization. The results are consistent with the previous observation (Ashby, B. and C. Frieden. 1977.J. Biol. Chem. 252:1869--1872) that AMP deaminase forms a tight complex in solution with subfragment-2 (S-2) of myosin or with heavy meromyosin (HMM).

AMP-deaminase from goldfish white muscle: regulatory properties and redistribution under exposure to high environmental oxygen level.

AMP-deaminase was partially purified from white skeletal muscle of goldfish, Carassius auratus. The enzyme was highly stable, showing virtually no change in activity at 1 month following the purification process when stored in 1 M KCl at 2-4 degrees C. The specific activity of the purified enzyme was 130-150 U/mg protein, with a pH optimum of about pH 6.5. AMP-aminohydrolase (AMPD) showed non-Michaelis-Menten kinetics, with a S(0.5) (half saturation by the substrate) for AMP of 0.73 +/- 0.03 mM, a Hill coefficient of 2.01 +/- 0.26, and a V(max) (maximum velocity) of 176 +/- 46 U/mg protein. Both sodium and potassium ions activated goldfish AMPD at low concentrations, with maximal activation at about 80 mM of each chloride salt, whereas higher concentrations became inhibitory. Magnesium and calcium ions also inhibited goldfish muscle AMPD, as did phosphate and fluoride; at a concentration of 8 mM, each anion reduced activity by about 66%. ADP and ATP were strong activators and both demonstrated concentration-dependent activation, with maximal effects at 0.5-1.5 mM. Fish exposure to a high concentration of oxygen (18-20 mg/l against 5-6 mg/l in the control) and recovery to the initial level induced a redistribution of AMPD between free and bound forms in goldfish white muscle and brain in a tissue-dependent manner. A spatial-temporal redistribution may be among the mechanisms regulating enzyme operation in vivo. Possible regulatory mechanisms of AMP-deaminase function in fish muscle are discussed.

Regulation of AMP-deaminase activity from white muscle of common carp Cyprinus carpio.

AMP-deaminase was purified to electrophoretic homogeneity from white skeletal muscle of a teleost fish, the common carp, Cyprinus carpio. The purified enzyme was highly stable and showed non-Michaelis-Menten kinetics with a S(0.5) value for AMP of 2.52+/-0.16 mM (SEM) and a Hill coefficient of 1.19+/-0.11. Specific activity of the purified enzyme was 1000-1200 U/mg protein. The pH optimum was 6.3 and the enzyme was activated by ADP and ATP, but inhibited by phosphate and fluoride. Low concentrations of NaCl and KCl (100-150 mM) activated, whereas higher concentrations were inhibitory. Free radicals inactivated the enzyme, decreasing V(max) by one-half but not affecting S(0.5) or Hill coefficient. Possible regulatory mechanisms of AMP-deaminase activity in fish muscle are discussed.

Overproduction, Purification and Characterization of Adenylate Deaminase from Aspergillus oryzae.

Adenylate deaminase (AMPD, EC 3.5.4.6) is an aminohydrolase that widely used in the food and medicine industries. In this study, the gene encoding Aspergillus oryzae AMPD was cloned and expressed in Escherichia coli. Induction with 0.75 mM isopropyl ß-D-l-thiogalactopyranoside resulted in an enzyme activity of 1773.9 U/mL. Recombinant AMPD was purified to electrophoretic homogeneity using nickel affinity chromatography, and its molecular weight was calculated as 78.6 kDa. Purified AMPD exhibited maximal activity at 35 °C, pH 6.0 and 30 mM K+, with apparent K m and V max values of 2.7 × 10-4 M and 77.5 µmol/mg/min under these conditions. HPLC revealed that recombinant AMPD could effectively catalyse the synthesis of inosine-5'-monophosphate (IMP) with minimal by-products, indicating high specificity and suggesting that it could prove useful for IMP production.

AMP deaminase from baker's yeast. Purification and some regulatory properties.

AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) was found in extract of baker's yeast (Saccharomyces cerevisiae), and was purified to electrophoretic homogeneity using phosphocellulose adsorption chromatography and affinity elution by ATP. The enzyme shows cooperative binding of AMP (Hill coefficient, nH, 1.7) with an s0.5 value of 2.6 mM in the absence or presence of alkali metals. ATP acts as a positive effector, lowering nH to 1.0 and s0.5 to 0.02 mM. P1 inhibits the enzyme in an allosteric manner: s0.5 and nH values increase with increase in Pi concentration. In the physiological range of adenylate energy charge in yeast cells (0.5 to 0.9), the AMP deaminase activity increases sharply with decreasing energy charge, and the decrease in the size of adenylate pool causes a marked decrease in the rate of the deaminase reaction. AMP deaminase may act as a part of the system that protects against wide excursions of energy charge and adenylate pool size in yeast cells. These suggestions, based on the properties of the enzyme observed in vitro, are consistent with the results of experiments on baker's yeast in vivo reported by other workers.

Changes in AMP deaminase activities in the hearts of diabetic rats.

AMP deaminase from normal and diabetic rat hearts was separated on cellulose phosphate and quantitated by HPLC. From soluble fractions three different AMP deaminase activities, according to KCl elution from cellulose phosphate and percent of total activity were: 170 mM (85%), 250 mM (8%) and 330 mM (7%) KCl. The AMP deaminase activity which eluted with 170 mM KCl was resolved to two distinct peaks by HPLC anionic exchange. After 4 weeks of diabetes the heart enzyme profile change to: 170 mM (10%), 250 mM (75%) and 330 mM (15%). Once purified the four activities were kinetically distinct: 170 mM KCl cytosolic, AMP Km = 1.78, stimulated by ATP, GTP, NADP and strongly inhibited by NAD; 170 mM KCl mitochondria AMP Km = 17.9, stimulated by ATP, ADP; 250 mM KCl isozyme, AMP Km = 0.66, stimulated by ADP; and 330 mM KCl isozyme, AMP Km = 0.97, inhibited by ATP, NAD(P).

Purification and properties of AMP-deaminase from human uterine smooth muscle.

AMP-deaminase from human uterine smooth muscle has been isolated, and properties of the enzyme were characterized. At pH 7.0, and in the presence of 100 mM potassium chloride the enzyme manifests a distinctly sigmoidal type of kinetics, with S0.5 parameter value about 12 mM. 1 mM ATP strongly activates the enzyme, and diminishes the value of S0.5 to 1.2 mM. In contrast to that 2.5 mM orthophosphate slightly inhibits the activity of AMP-deaminase studied and increases the S0.5 to about 14 mM. Similarly to ATP, orthophosphate does not influence the maximum velocity of the reaction. Electrophoresis in the presence of sodium dodecyl sulphate revealed that the molecular weight of human smooth muscle AMP-deaminase subunit is close to 37 kDa.

Purification and properties of AMP-deaminase from human uterine smooth muscle. Regulation by adenylate energy charge and activated fatty acids.

At pH 7.0 and physiological concentrations of the main regulatory ligands (ATP, ADP, orthophosphate), human uterine muscle AMP-deaminase follows a hyperbolic type of saturation kinetics with S0.5 parameter value about 2 mM. The enzyme is regulated by adenylate energy charge (AEC) variations, being the most active at the AEC value 0.5-0.6 or 0.5-0.7, depending on the size of the total adenine nucleotide pool. Long-chain acyl-CoA strongly inhibit activity of the enzyme, influencing mainly the maximum velocity of the reaction.

Isozymes of rat AMP deaminase.

Three AMP deaminase isozymes (EC 3.5.4.6 AMP aminohydrolase) were purified from rat heart, kidney and muscle. These enzyme preparations contained only the required isozyme. Antisera to individual isozymes were prepared and immunological relationships were tested. There was no cross-reactivity as tested by precipitation experiments. The antisera precipitated only the corresponding isozyme and there was no effect on other isozymes. These isozymes were also different in Km values for AMP and in substrate specificity. From the present studies, combined with previous results, it seems clear that the heart, kidney and muscle enzymes are different basic types. It is proposed that the muscle enzyme be designated as AMP deaminase A; the enzyme in kidney and liver, AMP deaminase B; the enzyme in heart, AMP deaminase C. Brain extracts contained five isozymes; two parent isozymes (B and C) and presumably their three hybrids.

Isolation by zinc-affinity chromatography of the histidine-proline-rich-glycoprotein molecule associated with rabbit skeletal muscle AMP deaminase. Evidence that the formation of a protein-protein complex between the catalytic subunit and the novel component is critical for the stability of the enzyme.

The histidine-proline-rich glycoprotein (HPRG) component of rabbit skeletal muscle AMP deaminase under denaturing and reducing conditions specifically binds to a Zn(2+)-charged affinity column and is only eluted with an EDTA-containing buffer that strips Zn(2+) from the gel. The isolated protein is homogeneous showing an apparent molecular weight (MW) of 95000 and the N-terminal sequence L-T-P-T-D-X-K-T-T-K-P-L-A-E-K-A-L-D-L-I, corresponding to that of rabbit plasma HPRG. The incubation with peptide-N-glycosidase F promotes the reduction of the apparent MW of isolated HPRG to 70000, characterizing it as a N-glycosylated protein. The separation from AMP deaminase of an 85-kDa component with a blocked N terminus is observed when the enzyme is applied to the Zn-charged column under nondenaturing conditions. On storage under reducing conditions, this component undergoes an 85- to 95-kDa transition yielding a L-T-P-T-D-X-K-T-T-K-P-L N-terminal sequence, suggesting that the shift in the migration on SDS/PAGE as well as the truncation of the protein at its N terminus are promoted by the reduction of a disulfide bond present in freshly isolated HPRG. The separation of HPRG induces a marked reduction in the solubility of AMP deaminase, strongly suggesting a role of HPRG in assuring the molecular integrity of the enzyme.

Phosphorylation of the skeletal muscle AMP-deaminase by protein kinase C.

Protein kinase C catalyzes phosphorylation of the rat skeletal muscle AMP-deaminase in the presence of calcium ions and phosphatidylserine. At the same time, the catalytic subunit of cAMP-dependent protein kinase fails to phosphorylate AMP-deaminase. Ca2+, phosphatidylserine-dependent phosphorylation decreases three-fold (from 0.6 to 0.2 mM) the Km value and does not affect Vmax. Protein kinase C-induced phosphorylation of AMP-deaminase, besides ADP-ribosylation, is suggested to be involved in regulating the AMP-deaminase activity in vivo.

Presence in human skeletal muscle of an AMP deaminase-associated protein that reacts with an antibody to human plasma histidine-proline-rich glycoprotein.

Histidine-proline-rich glycoprotein (HPRG) is a protein that is synthesized by parenchimal liver cells. The protein has been implicated in a number of plasma-specific processes, including blood coagulation and fibrinolysis. We have recently reported the association of an HPRG-like protein with rabbit skeletal muscle AMP deaminase (AMPD). The results of the immunological analysis reported here demonstrate that an antibody against human plasma HPRG reacts with an AMPD preparation from human skeletal muscle. To probe the localization of the putative HPRG-like protein in human skeletal muscle, serial sections from frozen biopsy specimens were processed for immunohistochemical and histoenzymatic stains. A selective binding of the anti-HPRG antibody to Type IIB muscle fibers was detected, suggesting a preferential association of the novel protein to the AMPD isoenzyme contained in the fast-twitch glycolytic fibers.

Purification and general properties of AMP deaminase from sheep brain.

AMP deaminase from sheep brain was purified to homogeneity on SDS-PAGE and its general properties were investigated. The native enzyme has a molecular weight of approximately 350,000 as estimated by gel filtration and it is composed of four identical subunits with a molecular weight of 85,000 each. The purified enzyme had a specific activity of 500 units/mg protein and shows a sigmoid-shaped AMP saturation curve in the presence of 100 mM KCl. This deaminase is strongly activated by ATP and inhibited by GTP. It slightly catalyzes the hydrolysis of adenosine monosulfate (AMS), dAMP, and adenosine phosphoramidate (APA). These catalytic properties resemble those of AMP deaminase from human liver.

Purification and regulatory properties of pig kidney AMP deaminase.

AMP deaminase (EC 3.5.4.6) from pig kidney was purified about 1200-fold by chromatography on cellulose phosphate. The enzyme showed a sigmoid-shaped substrate saturation curve which was converted to hyperbolic by addition of ATP. The ATP-activated enzyme was sensitive to phosphatidylcholine-containing liposomes which caused a further increase of activity by lowering the S0.5 value and increasing V max. In the absence of ATP, the enzyme was not sensitive to phosphatidylcholine-containing liposomes. Phosphatidate-containing liposomes exerted an inhibitory effect both in the presence and absence of ATP. In the presence of ATP phosphatidate was a non-competitive inhibitor. Orthophosphate was found to be a competitive inhibitor of AMP deaminase from pig kidney. When the phosphatidylcholine/phosphatidic acid ratio in liposomes was 2.7, AMP deaminase was activated, whereas when this ratio dropped below 2.1, liposomes exerted a non-competitive inhibitory effect.

Isolation and regulatory mechanisms of smooth muscle AMP-deaminase.

AMP-deaminase from cow uterine smooth muscle has been purified. The enzyme activity is regulated by the two cooperating mechanisms: allosteric and dissociation--association.

AMP deaminase from anterior lobe of bovine pituitary: purification and properties.

AMP deaminase (EC 3.5.4.6) from anterior lobe of bovine pituitary has been purified for the first time. Six molecular forms of the enzyme were eluted from phosphocellulose P11 with a KC1 concentration gradient. By two stage gel chromatography individual molecular forms were purified to electrophoretic homogeneity. Comparison of some physico-chemical and kinetic properties of the preparations obtained showed high similarity of their properties to those of AMP deaminase from other animal tissues already described. All the isoforms were found to be Zn(2+)-dependent.

Two forms of AMP deaminase in bovine heart.

Two forms of bovine heart AMP deaminase were separated by phosphocellulose column chromatography. Form A with lesser affinity to phosphocellulose exhibited a hyperbolic type of substrate curve and was relatively insensitive to ATP. Form B was strongly activated by 1 mM ATP and its substrate saturation kinetics (without ATP) indicated a cooperative effect. The alteration of adenylate energy charge affected forms A and B differently but within the physiological range, the activity of both forms decreased with the increase in energy charge. The Mr of the two forms was identical as estimated by gel filtration. These activities are compared to those of AMP deaminases from the hearts of other species.

Molecular forms of pigeon skeletal muscle AMP deaminase.

Phosphocellulose chromatography of pigeon leg muscle extract revealed the existence of two well-separated forms of AMP deaminase. This was in contrast to the pigeon breast muscle extract, which yielded only one form. The two leg muscle enzyme isoforms manifested similar kinetic and regulatory properties. They were activated by very low concentration of potassium ions and demonstrated similar patterns of pH and effector dependence. At pH 6.5, as well as at other pH values tested. ADP and ATP slightly stimulated, whereas GTP and orthophosphate inhibited the two molecular forms of pigeons leg muscle enzyme. Surprisingly, the molecular form of AMP deaminase present in pigeon breast muscle was inhibited by ATP at all pH values tested. The kinetic and regulatory properties of the three molecular forms of pigeon skeletal muscle AMP deaminase examined do not resemble those which have been described for pigeon heart muscle enzyme.

The application of affinity chromatography for the separation of "high Km" and "low Km" 5'-nucleotidase and other AMP metabolizing enzymes.

AMP-sepharose 4B has been widely used as a general ligand affinity chromatography for purification of AMP deaminase, 5'-nucleotidase, adenosine kinase and other adenine nucleotide metabolizing enzymes. Since these enzymes generally differ in their kinetic properties related to the values of Km for AMP and analogous compounds, it was assumed that there may be a specific elution pattern of some of the enzymes which would enable sequential elution from the column during a single run. Using 0.5 M NaCl, 10 mM ATP and 5 mM adenosine as eluting agents, it was possible to separate on AMP-sepharose column AMP deaminase "high Km" and "low Km" 5'-nucleotidase and adenosine kinase. Adenylate kinase, adenosine deaminase and nonspecific phosphatase did not bind to the column. Using human placental extract, AMP deaminase, "high Km" and "low Km" 5'-nucleotidase and adenosine kinase were purified 2.8, 2.9, 105 and 1240 fold, respectively. AMP deaminase and "high Km" 5'-nucleotidase were further separated using phosphocellulose column chromatography and the final purification was 227 and 143 fold, respectively. The specific activities of purified enzyme preparations were 9.1, 1.0, 0.4 and 0.5 mumols/min/mg protein of AMP deaminase, "high Km" 5'-nucleotidase and adenosine kinase, respectively. This approach provides a rapid method for initial purification of these enzymes from crude soluble extracts.

[Subunit structure of AMP-deaminase from skeletal muscles]. / Sub''edinichnoe stroenie AMP-dezaminazy skeletnykh myshts.

AMP-deaminase was purified from skeletal muscle of rat by the affinity chromatography on phosphocellulose and gel-filtration on Sephadex G-200. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE) has shown three protein bands on each step of purification. One of them corresponds to the subunit of tetrameric AMP-deaminase molecule with molecular weight of 76 kDa and two others--to the protein subunit with molecular weight of 42 and 33 kDa. Repeated SDS-PAGE of the main subunit band has revealed again all these protein bands. The data obtained indicate that AMP-deaminase subunit of 76 kDa is able to dissociate on two polypeptide chains with similar values of molecular weights in the presence of SDS.