Spectroscopic study of the Schiff bases of dodecylamine with pyridoxal 5′-phosphate and 5′-deoxypyridoxal. A model for the Schiff bases of pyridoxal 5′-phosphate in biological systems

Abstract

We recorded the absorption spectra of the Schiff bases of pyridoxal 5'-phosphate (PLP) and 5'-deoxypyridoxal (DPL) with dodecylamine (DOD) at different pH values. By applying deconvolution techniques to the spectra and analysing their different components we found that the above-mentioned Schiff bases in aqueous solutions of pH 7 adopted a conformation in which the pyridine ring is embedded in a very hydrophobic medium from which water is virtually completely excluded. This conformation in the same as that adopted by PLP when it acts as coenzyme for some enzymes such as glycogen phosphorylase. The experimental results obtained also show such a conformation to be highly favoured but sensitive to the protonation of the pyridine nitrogen, which makes the aromatic ring more readily accessible to the solvent.

Mutation of His465 Alters the pH-dependent Spectroscopic Properties of Escherichia coli Glutamate Decarboxylase and Broadens the Range of Its Activity toward More Alkaline pH

“…This is mainly substantiated by the persistence of the 420-nm absorbing ketoenamine species, typical of a more hydrated active site (5,32), which is still appreciably detected at pH Ͼ9.0.…”

Sulfur Mobilization in Cyanobacteria

“…4, right panels). The peak at 360 nm is likely the result of the deprotonation of the phenolic oxygen of the cofactor with formation of a dipolar species, as already observed for the PLP-dependent enzymes glycogen phosphorylase (49,50) and aspartate aminotransferase (51). The reaction proceeds with the accumulation of a species absorbing at 347 nm (Fig.…”

“…The second component accounts for a very small increase in absorbance at wavelengths lower than 340 nm, and the third component accounts for the transient species detected at 360 nm by single wavelength kinetics and originating from the 420 nm species. The transiently accumulated 360 nm band is likely attributable to a dipolar species of the cofactor directly formed from the 420 nm band (49,50,(72)(73)(74). Significantly, PLP-dependent enzymes where the dipolar species is predominant have evolved a network of ionic interactions aimed at stabilizing the positive charge on the pyridinium ring and the deprotonated phenolic oxygen (50,75).…”

Photo‐Induced Processes in Vitamin B6 Compounds

“…Schiff Base of e-Aminocaproic Acid with Pyridoxal 5'-Phosphate (PLP). We studied the Schiff base (SB) formed between PLP and e-aminocaproic acid, which has a formation constant of 10 at pH 4.6 and a value of 1000 on the pH range 8 ± 10 [12]. and 11.70 [12]) and exists as various tautomers in solution depending on the pH and polarity of the medium [12].…”