PMID: 7085661Jul 25, 1982Paper

A calorimetric study of the interaction of pyridoxal 5'-phosphate with aspartate apoaminotransferase and model compounds.

The Journal of Biological Chemistry
A GiartosioC Turano

Abstract

Schiff base formation between pyridoxal 5'-phosphate and model compounds of increasing complexity (i.e. L-valine and poly-L-lysine) and between pyridoxal 5'-phosphate and the apoenzyme of aspartate aminotransferase has been analyzed by microcalorimetric methods. The apparent pKa values and protonation enthalpy values for the relevant groups ionizing in the pH 4-9 range have been determined for the Schiff bases of L-valine and of poly-L-lysine. Upon Schiff base formation, the only noticeable change is the lowering of the ring nitrogen pK, accompanied by an increase of the relative delta H. In the poly-L-lysine Schiff base, however, the delta H relative to the protonation of the phosphate dianion becomes more negative. This behavior suggests a multiple interaction between the polymer and the ligand. The intrinsic heat of formation is small (congruent to -1 kcal/mol), of the same order of magnitude for both Schiff bases, and appears to be independent of the nature of the aminic reagent. The heat of reaction of pyridoxal 5'-phosphate with aspartate apoaminotransferase has been determined in the pH 6.2-8.8 range at 19 degrees C and at 25 degrees C. Each isotherm is characterized by a lack of proton evolution, a result that is unexpe...Continue Reading

Related Concepts

Metazoa
Apoenzymes
SGOT - Glutamate oxaloacetate transaminase
Calorimetry
Kinetics
Myocardium
Potentiometry
Plasma Protein Binding Capacity
Pyridoxal Phosphate
Schiff Bases

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