Binding and Reactions of the Vitamin B6 Coenzyme in the Catalytic Center of Aspartate Transaminase

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Publisher Summary This chapter surveys and discusses some results recently obtained in the laboratory in investigations relating to the mode of linkage and specific reactions of the vitamin B 6 coenzyme in the catalytic center of high-purity aspartate glutamate (AS)-transaminase. Inhibition analysis has already been exploited in different ways in the study of pyridoxal 5-phosphate (PLP) enzymes. A most rewarding current trend of enzyme chemistry is the design and application of plurifunctional inhibitors associating structural and configurational analogy to a substrate with capacity for covalent binding of an essential functional group of the apoenzyme. In research on PLP enzymes, particularly advantageous possibilities are afforded by combination of kinetic measurements with the use of spectrophotometric, spectrofluorometric, and spectropolarimetric methods for the study of interactions between the apo- or holoenzymes, on the one hand, and structural analogs of the coenzyme or of substrates, on the other. An obvious complication that limits the value of spectrophotometry for the investigation of reactions of PLP enzymes is the close similarity between absorption spectra of certain structural species of the enzymes and the spectra of enzyme-substrate and enzyme-inhibitor complexes.