Spectra and Ionization Constants of the Vitamin B6 Group and Related 3-Hydroxypyridine Derivatives1
01 May 1955-Journal of the American Chemical Society (American Chemical Society)-Vol. 77, Iss: 9, pp 2431-2437
About: This article is published in Journal of the American Chemical Society.The article was published on 1955-05-01. It has received 273 citations till now. The article focuses on the topics: Ionization.
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TL;DR: In the course of these investigations, a simple photometric method has been developed for the determination of pyridoxal or pyrIDoxal S-phosphate in enzymatic reaction mixtures and it is concluded that the two enzymes are probably identical.
517 citations
TL;DR: The results point to a static quenching mechanism operating in the complexes of 2-Pyridone, 3-pyridones, and 4-p Pyridone that is typical of tryptophan in a polar environment and are slightly reduced upon probe binding.
Abstract: Subdomain IIA binding site of human serum albumin (HSA) was characterized by examining the change in HSA fluorescence in the native, unfolded, and refolded states. The study was carried out in the absence and presence of small molecular probes using steady-state and time-resolved fluorescence measurements. 2-Pyridone, 3-pyridone, and 4-pyridone bear similar molecular structures to those found in many drugs and are used here as probes. They are found to specifically bind in subdomain IIA and cause a reduction in the fluorescence intensity and lifetime of the Trp-214 residue in native HSA which is located in the same subdomain. The efficiency of energy transfer from Trp-214 fluorescence to the probes was found to depend on the degree of the spectral overlap between the donor's fluorescence and the acceptor's absorption. After probe binding in subdomain IIA, the distance between the donor and acceptor was calculated using Forster theory. The calculated quenching rate constants and binding constants were also shown to depend on the degree of spectral overlap. The results point to a static quenching mechanism operating in the complexes. Denaturation of HSA in the presence of guanidine hydrochloride (GdnHCl) starts at [GdnHCl] > 1.0 M and is complete at [GdnHCl] > or = 6.0 M. Upon unfolding, two fluorescence peaks were observed. One peak was assigned to the fluorescence of Trp-214 in a polar environment, and the other peak was assigned to tyrosine fluorescence. A reduction of the fluorescence intensity of the two peaks upon binding of the probes to the denatured HSA indicates that Tyr-263 in subdomain IIA is one of the tyrosine residues responsible for the second fluorescence peak. The results were confirmed by measuring the fluorescence spectra and lifetimes of denatured HSA at different excitation wavelengths, and of L-tryptophan and L-tyrosine free in buffer. The measured lifetimes of denatured HSA are typical of tryptophan in a polar environment and are slightly reduced upon probe binding. Dilution of the denatured HSA by buffer results in a partial refolding of subdomain IIA. This partial refolding is attributed to some swelling of the binding site caused by water. The swelling prevents a full recovery from the denatured state.
455 citations
TL;DR: The data suggest that the compound isolated in bovine achilles tendon collagen is a 3-hydroxypyridinium derivative with three amino acid side chains, which is a novel type crosslink of collagen.
291 citations
TL;DR: This chapter examines some of the questions about structural features required for vitamin B6 activity in living organisms and what chemical features determine the ability of the coenzyme to participate in catalysis of the reactions for which it is essential.
Abstract: Publisher Summary This chapter examines some of these questions with respect to vitamin B6. The problem can be considered from three points of view: (1) what are the structural features required for vitamin B6 activity in living organisms, (2) what structural features determine the ability of a compound to serve as a coenzyme for vitamin B6-dependent enzymes, and (3) apart from ability to combine with its conjugate apoenzymes, what chemical features determine the ability of the coenzyme to participate in catalysis of the reactions for which it is essential? These questions can be profitably considered in reverse order because unless the chemical prerequisites for participation in catalysis are present, a compound obviously will be of no value as a coenzyme, however closely it may resemble the coenzyme in other respects. By the same token, it cannot serve as a vitamin, the sole function of which is to serve as a precursor for coenzyme formation.
256 citations
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