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A Raggi

Publications and source records attributed to A Raggi.

At least 37 records · Page 2Linked to original sources
PubMed1979

Negative homotropic cooperativity in rat muscle AMP deaminase. A kinetic study on the inhibition of the enzyme by ATP.

1. Rat skeletal muscle AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) at optimal KCl concentrations shows a biphasic response to increasing levels of the allosteric inhibitor ATP. 2. Up to 10 micrometer, ATP appears to convert the enzyme to a form exhibiting sigmoidal kinetics while at higher concentrations its inhibitory effect is manifested by an alteration of AMP binding to AMP deaminase indicative of negative homotropic cooperativity at about 50% saturation. 3. AMP deaminase is inactivated by incubation with the periodate oxidation product of ATP. The (oxidized ATP)--AMP deaminase complex stabilized by NaBH4 reduction shows kinetic properties similar to those of the native enzyme in the presence of high ATP concentrations. 4. A plausible explanation of the observed cooperativity is that ATP induces different conformational state of AMP deaminase subunits, causing the substrate to follow a sequential mechanism of binding to enzyme. 5. Binding of the radioactive oxidized ATP shows that 3.2 mol of this reagent bind per mol AMP deaminase.

AMP Deaminase↗
PubMed1976

Specific modification of the GTP binding sites of rat 5'-adenylic acid aminohydrolase by periodate-oxidized GTP.

1. Rat skeletal muscle AMP deaminase (AMP aminohydrolase, EC3.5.4.6) can be inactivated by incubation with the periodate-oxidized analogue of the enzyme inhibitor GTP. 2. Nucleoside triphosphates and KCl at high concentrations protect against inactivation, while ADP has no effect. 3. The inactivation can be reversed by the addition of GTP and amino acids and made irreversible by reduction with NaBH4. This indicates that, in the binding of the oxidized GTP to the enzyme, a Schiff base is formed between the aldehyde groups of the inhibitor and amino groups of the enzyme. 4. The kinetic properties of the reduced (oxidized GTP)-AMP deaminase derivative indicate that the loss of activity results from an increase in Km while no appreciable change in V is observed; consequently, the enzyme shows positive homotropic cooperativity even in the presence of optimal KCl concentration. 5. Since the treated enzyme shows kinetic properties similar to those of the native enzyme in the presence of GTP, and since the loss of sensitivity to GTP is directly proportional to the degree of inactivation, it is concluded that the oxidized GTP specifically modifies the binding sites for GTP. 6. Binding of the radioactive oxidized GTP shows that two binding sites for this reagent exist in the AMP deaminase molecule.

AMP Deaminase↗
PubMed1975

The nature of inactivation of rat muscle 5'-adenylate aminohydrolase by fluorodinitrobenzene.

1. The inactivation of rat skeletal muscle AMP deaminase by Dnp-F (1-fluoro-2,4-dinitrobenzene) is accompanied by the arylation of thiol, amino and phenolic hydroxyl groups. 2. The number of thiol groups that react with Dnp-F is about 12; this is the number that reacts with Nbs2 [5,5'-dithiobis-(2-nitrobenzoic acid)] and N-ethylmaleimide without loss of enzyme activity, and it appears to be the same thiol groups that all three reagents attack. 3. Dinitrophenylation of these reactive SH groups is not the cause of inactivation, since active N-ethylmaleimide-substituted enzyme is also inactivated by Dnp-F.4. Complete inactivation of the N-ethylmaleimide-treated AMP deaminase occurs when about six tyrosine and two lysine residues are dinitrophenylated. 5. Since the treatment of Dnp-enzyme with 2-mercaptoethanol restores much of the enzyme activity, inactivation of AMP deaminase by Dnp-F is probably largely due to modification of tyrosine residues. 6. The kinetic properties of the Dnp-enzyme indicate that a marked decrease in V occurs only after extensive enzyme modification. The decreased activity after slight inactivation results from modification of Km.

AMP Deaminase↗