Cytosolic aspartate amino transferase

Even with high M.W. enzymes labeling coenzyme e.g. ( CHO-PLP) can give excellent results. Thus the use of C-labeled coenzyme in the reactions catalyzed by cytosolic aspartate amino transferase (EC 2.6.1.1) a dimeric protein (Mj. 90,(XX)), allows clear observation of both internal and external aldimine forms with inhibitors such as methyl aspartate as shown in Fig. 13 [9]. 

T. Oka, N. Komori, M. Kuwahata, Y. Hiroi, T. Shimoda, M. Okada, and Y. Natori. Pyridoxal 5 -phosphate modulates expression of cytosolic aspartate amino-transferase gene by inactivation of glucocorticoid receptor. J. Nutr. Sci. Vitaminol. 41 363-375 (1995). 

Similar results were obtained in Yon s laboratory with aspartate amino transferase from pig heart cytosol, which is a dimer with one PLP bound per subunit. A strong anticooperativity for binding of pyridoxamine phosphate (PMP) was reported (Arrio-Dupont, 1972). In the haloenzyme-apoenzyme hybrid an important decrease of reactivity of Cys 190 (which is entirely accessible in apoenzyme and buried in holoenzyme) also indicated strong coupling between protomers in the enzyme molecule (Cournil, 1975 Cournil and Arrio-Dupont, 1975). Dissociation of the apoenzyme by dilution was... 

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