Remarks concerning the dispute related to the function of plant glutamate dehydrogenase: Commentary

Abstract

A dispute on the function of plant glutamate dehydrogenase (GDH) highlighted in two recent commentaries in the Canadian Journal of Botany (Oaks 1995; Fox et al. 1995) is as old as glutamate dehydrogenase (GDH) research itself (Bulen 1956; Davies and Teixeira 1975). It involves the question, Is the mitochondrial GDH functioning as a primary reaction of ammonia assimilation or does it catalyze the catabolic degradation of glutamate? Perhaps phrasing the question in this way only leads to a wrong research emphasis and as a result improved experimental approaches, like the powerful NMR technique, will only decipher pieces of the truth. From my point of view the current dispute cannot be settled by continuing with experiments along established research paths. I would go further and suggest that the supposed experimental where J is the net flux, k is the rate constant of the reaction or reacting system, and A is the thermodynamic driving force (the deviation from equilibrium) of the process. Hence A describes the reaction gradient of a reaction under a given metabolic environment that is followed by a flux. Knowledge about A is of importance in resolving the current dispute and will be the focus of my considerations. In accordance with biochemical practice, A is written as depicted in eq. 2, which is chosen to be the generalized form of the bi-ter GDH reaction (for details concerning A see Segel 1975), as