UV SPECTRAL CHARACTERISTICS AND ACIDIC DISSOCIATION CONSTANTS OF 280 ALKYL BASES, NUCLEOSIDES, AND NUCLEOTIDES

2010 ◽  
pp. 255-262
Author(s):  
B. Singer
Keyword(s):  
Dissociation Constants ◽  
Spectral Characteristics ◽  
Acidic Dissociation

Determination of acidic dissociation constants of L-phenylalanyl-glycine and L-alanyl-L-alanine in water using ab initio methods

2014 ◽  
Vol 2 (42) ◽  
pp. 263-263
Author(s):  
Farhoush Kiani ◽  
Mahmoud Tajbakhsh ◽  
Fereydoon Ashrafi ◽  
Nesa Shafiei ◽  
Azar Bahadori ◽  
...  
Keyword(s):  
Ab Initio ◽  
Dissociation Constants ◽  
Ab Initio Methods ◽  
Acidic Dissociation

scholarly journals A Theoretical Study on Determination of Acidic Dissociation Constants of Penicillamine and Captopril in Water

2014 ◽  
Vol 4 (1) ◽  
pp. 018-032 ◽  
Author(s):  
Kiani Farhoush ◽  
◽  
Taherinasab R ◽  
Tahermansouri Hasan ◽  
Koohyar Fardad ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Dissociation Constants ◽  
Acidic Dissociation

The acidic dissociation constants of mandelic acid

1961 ◽  
Vol 48 (17) ◽  
pp. 571-571 ◽  
Author(s):  
B. Csisz�r ◽  
M. Halmos ◽  
M. T. Beck
Keyword(s):  
Mandelic Acid ◽  
Dissociation Constants ◽  
Acidic Dissociation

Interactions of Calf Spleen Purine Nucleoside Phosphorylase with 8-Azaguanine, and a Bisubstrate Analogue Inhibitor: Implications for the Reaction Mechanism

2004 ◽  
Vol 59 (9-10) ◽  
pp. 713-725 ◽  
Author(s):  
Jacek Wierzchowski ◽  
Agnieszka Bzowska ◽  
Katarzyna Stępniak ◽  
David Shugar
Keyword(s):  
Purine Nucleoside Phosphorylase ◽  
Dissociation Constants ◽  
Reaction Pathway ◽  
Spectral Characteristics ◽  
Difference Spectrum ◽  
Purine Nucleoside ◽  
Fluorimetric Determination ◽  
Kinetic Measurements ◽  
Nucleoside Phosphorylase ◽  
Synthetic Reaction

Abstract Interactions of calf spleen purine nucleoside phosphorylase (PNP) with a non-typical substrate, 8-azaguanine (8-azaG), and a bisubstrate analogue inhibitor, 9-(2-phosphonylmethoxyethyl)- 8-azaguanine (PME-azaG), were investigated by means of steady-state fluorescence spectroscopy. Both 8-azaG and PME-azaG form fluorescent complexes with the enzyme, and dissociation constants are comparable to the appropriate parameters (Km or Ki) obtained from kinetic measurements. PME-azaG inhibits both the phosphorolytic and synthetic pathway of the reaction in a competitive mode. The complex of 8-azaG with PNP is much weaker than the previously reported Gua-PNP complex, and its dissociation constant increases at pH > 7, where 8-azaG exists predominantly as the monoanion (pKa ≈ 6.5). The fluorescence difference spectrum of the PNP/8-azaG complex points to participation of the N(7)H or/and N(8)H tautomers of the neutral substrate, and the 9-(2-phosphonylmethoxyethyl) derivative also exists as a neutral species in the complex with PNP. The latter conclusion is based on spectral characteristics of the PNP/PME-azaG complex, confirmed by fluorimetric determination of dissociation constants, which are virtually pH-independent in the range 6-7. These findings testify to involvement of the neutral purine molecule, and not its monoanion, as the substrate in the reverse, synthetic reaction. It is proposed that, in the reverse reaction pathway, the natural purine substrate is bound to the enzyme as the neutral N(7)H tautomer, which is responsible for the reported strong fluorescence of the guanine-PNP complex.

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