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3. The Activation of β-Galactosidase by Divalen and Monovalent Cations.

Author

Strom, Roberto, Attardi, Domenica Gandini, Forsén, Sture, Turini, Paola, Celada, Franco, and Antonini, Eraldo

Subjects
*CATIONS, *CARBENES, *ENZYMES, *PROTEINS, *CATALYSTS, *SURFACE chemistry
Abstract

The activation of Escherichia coli K12 3300 β-galactosidase by Na+ and Mg2+ ions appears to involve, apart from effects on the catalytic rate, a complex pattern of interaction between the substrate and the two cations. The time course of activation by Mg2+ can be followed directly by rapid mixing methods; m the presence of Na+ the kinetics of this process is complex, due to the presence of a monomolecular step which becomes rate limiting at high reagent concentrations. The effects produced by Na+, on the other hand, occur rapidly in comparison with the highest attainable rates of catalysis. The activity of defective enzymes from lac- point mutants is also Na+- and Mg2+-dependent. [ABSTRACT FROM AUTHOR]

Published
1971
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4. Binding and cleavage of pre-tRNA by the Xenopus splicing endonuclease: Two separable steps of the intron excision reaction

Author

Baldi, Maria Irene, Mattoccia, Emilio, Ciafrè, Stefania, Attardi, Domenica Gandini, and Tocchini-Valentini, Glauco P.

Abstract

We have constructed three base-substitution mutants of the yeast tRNALeu3gene. In two of them the ability to form an extended anticodon stem is lost. In the first mutant the bases encoding the anticodon change from TTG to GAC (positions 37, 36, 35); in the second, the nucleotides encoding the region of the intron that base-pair with the anticodon change from CAA to GTC (positions 48, 47, 46). The third is a double mutant characterized by both substitutions described above so that its ability to form an extended anticodon stem is restored. The precursors derived from the two single mutants are accurately spliced in the X. laevis germinal vesicles (GV) extract: pairing of the anticodon with the intron, therefore, is not required for the splicing reaction. The precursor derived from the double mutant is not spliced, indicating that the new extended anticodon stem exerts an inhibitory action. Since the double mutant precursor binds to the purified splicing endonuclease, binding and cleavage occur as two separable steps in the intron excision reaction.

Published
1986
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