Browsing by Author "delVado, MAG"

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    Determination of the rates of formation and hydrolysis of the Schiff bases formed by 5'-deoxypyridoxal and poly-L-lysine
    (ELSEVIER SCIENCE BV, 1997) delVado, MAG; Echevarria, GR; Blanco, JGS; Blanco, FG
    The kinetics of the reaction between 5'-deoxypyridoxal (DPL) and poly-L-lysine in aqueous solutions at a variable pH and a constant ionic strength of 0.1 M was studied spectrophotometrically. The rate constants of formation and hydrolysis of the resulting Schiff base and its stability constant at a variable pH were also determined. A comparison of the formation rate constant for the Schiff base with those for the models of pyridoxal 5'-phosphate (PLP) with poly-L-lysine and DPL with n-hexylamine revealed the effect of both the phosphate group of PLP and of the polypeptide chain on intramolecular catalysis in the dehydration of the intermediate carbinolamine formed. The effects of the polypeptide and the phosphate group on the hydrolysis of the Schiff base and hence on the base stability are also demonstrated.
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    Kinetics of the formation and hydrolysis of the Schiff bases of pyridoxal 5'-phosphate and copolypeptides containing L-lysine and aromatic L-amino acids
    (1996) delVado, MAG; Perez, MPM; Cardona, AFR; Echevarria, GR; Blanco, JGS; Blanco, FG
    We determined the apparent rate constants of formation (k(1)) and hydrolysis (k(2)) of the Schiff bases formed between pyridoxal 5'-phosphate and copolymers of L-lysine-L-tyrosine and L-lysine-L-phenylalanine, at different pH values, at temperature of 25 degrees C and an ionic strength of 0.1 M. The values of the rate constant of formation obtained for the systems of the present work are greater than these for the PLP-poly-L-lysine system in all the range of pH studied, due to the presence of aromatic groups in the lateral chains of the polypeptide. The existence of these groups favors the presence of a few polar environment for the Schiff bases.
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    Schiff bases of poly-L-lysine and some compounds of the vitamin B-6 group. Influence of polypeptidic structure
    (ELSEVIER SCIENCE BV, 1997) delVado, MAG; Gorostidi, GRE; Blanco, JGS; Blanco, FG
    The apparent rate constants of formation (k(1)) and hydrolysis (k(2)) of the Schiff bases formed between pyridoxal and poly-L-lysine has been fitted to a kinetic scheme that involves the different protonated species in the reaction medium and the individual rate constants of formation (k(1)(i)) and hydrolysis (k(2)(i)). A Bronsted plot with alpha = 0.67 is in accord with an acid catalytic intramolecular process. The effects of hydrophobic medium due to the presence of the macromolecule on the formation and hydrolysis of Schiff bases from FL, DPL and PLP with poly-L-lysine is discussed.