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23. Chemical modification of pig kidney 3,4-dihydroxyphenylalanine decarboxylase with diethyl pyrocarbonate. Evidence for an essential histidyl residue.

Author

Dominici, P, Tancini, B, and Borri Voltattorni, C

Abstract

Diethyl pyrocarbonate inhibits pig kidney holo-3,4-dihydroxyphenylalanine decarboxylase with a second-order rate constant of 1170 M-1 min-1 at pH 6.8 and 25 degrees C, showing a concomitant increase in absorbance at 242 nm due to formation of carbethoxyhistidyl derivatives. Activity can be restored by hydroxylamine, and the pH curve of inactivation indicates the involvement of a residue with a pKa of 6.03. Complete inactivation of 3,4-dihydroxyphenylalanine decarboxylase requires the modification of 6 histidine residues/mol of enzyme. Statistical analysis of the residual enzyme activity and of the extent of modification shows that, among 6 modifiable residues, only one is critical for activity. Protection exerted by substrate analogues, which bind to the active site of the enzyme, suggests that the modification occurs at or near the active site. The modified inactivated 3,4-dihydroxyphenylalanine decarboxylase still retains most of its ability to bind substrates. Thus, it may be suggested that the inactivation of enzyme by diethyl pyrocarbonate is not due to nonspecific steric or conformational changes which prevent substrate binding. However, the modified enzyme fails to produce at high pH either an enzyme-substrate complex or an enzyme-product complex absorbing at 390 nm. Considerations on this peculiar feature of the modified enzyme consistent with a catalytic role for the modified histidyl residue are discussed. The overall conclusion of this study may be that the modification of only one histidyl residue of 3,4-dihydroxyphenylalanine decarboxylase inactivates the enzyme and that this residue plays an essential role in the mechanism of action of the enzyme.

Published
1985
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24. The binding of the coenzyme pyridoxal 5'-phosphate and analogues of the substrate-coenzyme complex to tyrosine decarboxylase

Author

Orlacchio, A, Borri-Voltattorni, C, and Turano, C

Abstract

Phosphopyridoxyl derivatives, which are stable analogues of a substrate-coenzyme complex, are bound at the active site with great affinity. From a comparison of the interaction of a number of such compounds with the apoenzyme the delta G0 values for the binding of the substrate carboxy and phenyl groups and of the coenzyme aldehydic group were determined to be equal to (or more negative than) ‒3.8. ‒8.4 and ‒12.5kJ/mol (-0.9, ‒1.9 and ‒3kcal/mol) respectively; the delta G0 for the binding of the coenzyme phosphate group was shown to be more negative than ‒20.5kJ/mol (-4.9kcal/mol). Two features of the binding process of the coenzyme-substrate analogues to tyrosine decarboxylase have already been found in the case of tyrosine aminotransferase [Borri-Voltattorni, Orlacchio, Giartosio, Conti & Turano (1975) Eur. J. Biochem. 53, 151-160]: (1) in the binding of the substrate to the enzyme a significant fraction of the instrinsic delta G0 appears to be used for some associated endoergonic process; (2) the delta H0 and delta S0 of binding appear to be very sensitive indicators of the correct alignment of the substrate-coenzyme and analogues at the active site.

Published
1980
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27. The Binding of the Coenzyme Pyridoxal 5'-Phosphate and Analogues of the Substrate-Coenzyme Complex to Tyrosine Decarboxylase

Author

Carlo Turano, Borri-Voltattorni C, and A Orlacchio

Subjects
Stereochemistry, Coenzymes, Biochemistry, Cofactor, chemistry.chemical_compound, Structure-Activity Relationship, Tyrosine aminotransferase, Mole, Molecular Biology, Tyrosine Transaminase, chemistry.chemical_classification, Binding Sites, biology, Chemistry, Temperature, Active site, Substrate (chemistry), Cell Biology, Tyrosine Decarboxylase, Phosphate, Tyrosine decarboxylase, Kinetics, Enzyme, Pyridoxal Phosphate, biology.protein, Thermodynamics, Research Article
Abstract

Phosphopyridoxyl derivatives, which are stable analogues of a substrate-coenzyme complex, are bound at the active site with great affinity. From a comparison of the interaction of a number of such compounds with the apoenzyme the delta G0 values for the binding of the substrate carboxy and phenyl groups and of the coenzyme aldehydic group were determined to be equal to (or more negative than) ‒3.8. ‒8.4 and ‒12.5kJ/mol (-0.9, ‒1.9 and ‒3kcal/mol) respectively; the delta G0 for the binding of the coenzyme phosphate group was shown to be more negative than ‒20.5kJ/mol (-4.9kcal/mol). Two features of the binding process of the coenzyme-substrate analogues to tyrosine decarboxylase have already been found in the case of tyrosine aminotransferase [Borri-Voltattorni, Orlacchio, Giartosio, Conti & Turano (1975) Eur. J. Biochem. 53, 151-160]: (1) in the binding of the substrate to the enzyme a significant fraction of the instrinsic delta G0 appears to be used for some associated endoergonic process; (2) the delta H0 and delta S0 of binding appear to be very sensitive indicators of the correct alignment of the substrate-coenzyme and analogues at the active site.

Published
1980

47. DNA methylating activity in murine lymphoma cells treated with xenogenizing chemicals

Author

Puccetti P, Allegrucci M, Borri Voltattorni C, Luigina Romani, Dominici P, and Mc, Fioretti

Subjects
Male, Mice, Azacitidine, Animals, Mice, Inbred Strains, DNA, Neoplasm, Triazenes, Leukemia L1210, Carmustine, Methylation, Neoplasm Transplantation
Abstract

We investigated whether epigenetic rather than mutational events might be involved in the induction of immunogenicity by the triazene derivative 1-(p-chlorophenyl)-3,3-dimethyltriazene (DM-Cl). To this purpose, we assessed the DNA methylation pattern of murine lymphoma cells xenogenized by DM-Cl and compared it with the changes induced by the DNA hypomethylating agent 5-azacytidine (5-Aza), which is also capable of affecting tumor cell immunogenicity. Both agents were found to increase the immunogenic potential of the treated tumor but according to different modalities. In particular, the novel immunogenicity conferred by 5-Aza treatment correlated well with the extent of hypomethylation induced, as opposed to what was observed for tumor xenogenization by DM-Cl.

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