Binding of pyridoxal, pyridoxal 5′-phosphate and derived hydrazones to bovine serum albumin in aqueous solution

Isothermal titration calorimetry investigation of the interactions between vitamin B6-derived hydrazones and bovine and human serum albumin

“…Other stoichiometries and their combinations were tested but were always rejected by the software. The stability of the complexes with BSA increases from PLP-PRZ and PLP-INH to PLP-2FH as previously observed by spectrofluorimetric experiments [14]. An opposite trend was found for the HSA-hydrazone systems and this evidence could be ascribed to the diverse interactions of the ligands with slightly different domains of the two serum proteins [42].…”

“…The secondary structure of albumin is altered during the reaction with the hydrazones, as it was determined using IR-spectroscopy [14], and other small molecules, as indicated by a mismatch of the van't Hoff enthalpy value with that measured experimentally by ITC [45]. The change in the secondary structure of the protein has its own change in enthalpy [46][47][48], which results in additional heat evolving or absorbing during each injection of the titrant.…”

“…These heat effects are dependent on the degree of change in the secondary structure of the protein and, therefore, the net heats of reaction may contain inaccuracies or supplementary contributions from side processes which is hard to take into account. For this reason, the logK values obtained from fluorimetry [14] and ITC experiments may show some differences. The dependence of both binding constant and change in enthalpy on the concentration of background electrolytes or dissolved organic compounds is a known phenomenon; for example, some authors reported the changes in α-helices content in lysozyme upon addition of NaCl and the corresponding decrease in logK and increase in ΔH r [49].…”

“…The circular dichroism technique showed that the addition of the hydrazone to the protein causes an insignificant change in its secondary structure [13]. The binding constants for a number of pyridoxal-5-phosphate-derived hydrazones with BSA were determined using spectrofluorimetric experiments [14]; however, the thermodynamic parameters and the binding forces for the interaction of these hydrazones obtained from vitamin B 6 with albumins in solution are still lacking.…”

Dephosphorylation of pyridoxal 5′‐phosphate‐derived Schiff bases in the presence of bovine alkaline phosphatase

“…12,13 Though the stability constants of d-metal complexes with PLP-and PL-derived hydrazones defining their biological activity are similar in neutral aqueous solution, 14,15 the equilibrium constants of binding of different B 6 vitamers and their hydrazones to serum albumins differ. 16,17 Schiff bases formed by PL are also less soluble than those of PLP since the phosphate group capable of dissociating twice is substituted by less acidic proton. Therefore, the enzymatic dephosphorylation of pyridoxal 5′phosphate derivatives is probably an important step of hydrazones metabolism in either liver or guts influencing their bioavailability and/or excretion.…”