THE REACTION OF GLYOXYLATE WITH TRIS BUFFER UNDER PHYSIOLOGICAL CONDITIONS

The importance of amino acid interactions in the crystallization of hydroxyapatite

Non-collagenous proteins (NCPs) inhibit hydroxyapatite (HA; Ca(5)(PO(4))(3)OH) formation in living organisms by binding to nascent nuclei of HA and preventing their further growth. Polar and charged amino acids (AAs) are highly expressed in NCPs, and the negatively charged ones, such as glutamic acid (Glu) and phosphoserine (P-Ser) seem to be mainly responsible for the inhibitory effect of NCPs. Despite the recognized importance of these AAs on the behaviour of NCPs, their specific effect on HA crystallization is still unclear, and controversial results have been reported concerning the efficacy of HA inhibition of positively versus negatively charged AAs. We focused on a positively charged (arginine, Arg) and a negatively charged (Glu) AA, and their combination in the same solution. We studied their inhibitory effect on HA nucleation and growth at physiological temperature and pH and we determined the mechanism by which they can affect HA crystallization. Our results showed a strong inhibitory effect of Arg on HA nucleation; however, Glu was more effective in inhibiting HA crystal growth during the growth stage. The combination of Glu and Arg was less effective in controlling HA nucleation, but it inhibited HA crystal growth. We attributed these differences to the stability of complexes formed between AAs and calcium and phosphate ions at the nucleation stage, and in bonding strength of AAs to HA crystal faces during the growth stage. The AAs also influenced the morphology of synthesized HA. Presence of either Arg or Glu resulted in the formation of spherulites consisting of preferentially oriented nanoplatelets orientation. This was attributed to kinetic factors favoring growth front nucleation (GFN) mechanism.

Influence of Tris(hydroxymethyl)aminomethane on kinetic mechanism of yeast alcohol dehydrogenase

Acetaldehyde, propionaldehyde, glyceraldehyde-3-P and 4-dimethylaminocinnamaldehyde form Schiff bases in Tris. HCl buffers; the rates of formation and dissociation of Schiff bases, and equilibrium constants for their formation are very similar for the first three aldehydes. The steady-state kinetic constants for the yeast alcohol dehydrogenase-catalyzed reaction, propan-1-ol + NAD+ reversible propionaldehyde + NADH + H+, have been determined in several Tris. HCl buffers of increasing concentration at pH 8.1. In the forward direction, oxidation of alcohol, most kinetic constants are increased by increasing concentrations of Tris. In the reverse direction, reduction of aldehyde, substrate, NADH, Tris and Schiff base were equilibrated before enzyme reaction was started. It was found that Schiff base, rather than Tris, binds to free enzyme competitively with respect to NADH. Tris and Schiff base do not influence the binding of aldehyde to enzyme in any way.

Enzymatic measurement of ethanol or NAD in acid extracts of biological samples

An enzymatic method for the measurement of ethanol has been developed to permit analyses with unneutralized acid extracts of blood, liver, cell suspensions, or other biological materials. Components of the assay mixture include NAD, yeast alcohol dehydrogenase, tris(hydroxymethyl)aminomethane (Tris), and lysine. Tris is a trapping agent for the reaction product, acetaldehyde. Lysine is used to maintain the pH at 9.7 where oxidation of ethanol is quantitative and most rapid, even when as much as 0.2 ml of 0.5 N HClO4 is added. Lysine also causes the reaction to be 2 to 4 times faster than it is when either glycine or 2-amino-2-methyl-1-propanol is used as the buffer. The assay is linear up to an ethanol concentration of 0.125 mM in the reaction mixture and is complete by 4 min. By substituting ethanol for NAD in the reagents, the assay performs equally well in measuring NAD.

The specificities and configurations of ternary complexes of yeast and liver alcohol dehydrogenases

1. Some aspects of the substrate specificities of liver and yeast alcohol dehydrogenases have been investigated with pentan-3-ol, heptan-4-ol, (+)-butan-2-ol, (+/-)-butan-2-ol, (+/-)-hexan-3-ol and (+/-)-octan-2-ol as potential substrates. The liver enzyme is active with all substrates tested, including both isomers of each optically active alcohol. In contrast, the yeast enzyme is completely inactive towards those secondary alcohols where both alkyl groups are larger than methyl and active with only the (+)-isomers of butan-2-ol and octan-2-ol. 2. The absence of stereospecificity of liver alcohol dehydrogenase towards optically active secondary alcohols and its broad specificity towards secondary alcohols in general are explained in terms of an alkyl-binding site that will react with a variety of alkyl groups and the ability of the enzyme to accommodate a fairly large unbound alkyl group in an active enzyme-NAD(+)-secondary alcohol ternary complex. The absolute optical specificity of the yeast enzyme towards n-alkylmethyl carbinols and its unreactivity towards pentan-3-ol, hexan-3-ol and heptan-4-ol are explained by its inability to accept alkyl groups larger than methyl in the unbound position in a viable ternary complex. 3. Comparison of the known configurations of the n-alkylmethyl carbinols and [1-(2)H]ethanol and [1-(3)H]geraniol, which have been used in stereospecificity studies with these enzymes by other workers, provides strong evidence for which alkyl group of the substrate is bound to the enzyme in the oxidation of n-alkylmethyl carbinols. The conclusions reached are, for butan-2-ol oxidation with the liver enzyme, confirmed by deductions from kinetic data obtained with (+)-butan-2-ol and a sample of butan-2-ol containing 66% of (-)-butan-2-ol. 4. Initial-rate parameters for the oxidations of (+)-butan-2-ol, 66% (-)-butan-2-ol and pentan-3-ol by NAD with liver alcohol dehydrogenase are presented. The data are completely consistent with a general mechanism of catalysis previously proposed for this enzyme.