The Interaction of Glutamate Dehydrogenase and Malate Dehydrogenase with Phospholipid Membranes

Abstract

The interaction between sonicated dispersions of purified phospholipids, corresponding to those found in the inner mitochondrial membrane, and the enzymes was studied by kinetic and spectroscopic methods.With glutamate dehydrogenase the charge type of the lipid head group determines the extent of lipid-protein complexing. Phosphatidylcholine did not significantly alter the activity of the enzyme a t lipid concentrations up to 1 mM, and the nuclear magnetic resonance (NMR) spectrum of the lipid (lolo, w/v) was not altered in the presence of enzyme (up to 2O/,, w/v).Phosphatidylethanolamine did not affect the activity in the oxidation of glutamate, but interfered with the assay in the reverse direction, possibly owing to Schiff-base formation with 2-oxoglutarate. The negatively charged cardiolipin, which is found uniquely in the inner mitochondrial membrane, strongly and reversibly inhibited the enzyme (50 O/,, inhibition with 0.1 -20 pM lipid, depending on conditions). Another anionic phospholipid, phosphatidylserine (which does not occur in mitochondria), also inhibited the enzyme, but less effectively (50°/, inhibition a t about 8 pM). The lipid-enzyme interaction decreases with increasing ionic strength, indicating an electrostatic contribution to the binding. NMR studies suggest that there is also an apolar interaction involving the lipid chains.The studies with malate dehydrogenase concentrated on detecting possible stabilization of this enzyme through interaction with lipids. A clear-cut stabilization was found with lysophosphatidylcholine. Under conditions such that the enzyme alone lost 50°/, on the initial activity in about 2 h, lysophosphatidylcholine gave a slight (2O0lO) activation and this activity remained constant for several hours. NMR studies indicated that, as with the related enzyme 3-hydroxybutyrate dehydrogenase, both the polar choline head group and the hydrocarbon chains are involved in the binding of the lipid to the protein.These specific lipid * protein complexes are probably examples of allotopic interactions. This form of complexing may explain aspects of the behaviour of these enzymes in vivo.The allosteric interactions of enzyme systems have been extensively studied both experimentally and theoretically and these interactions are now &mly established as a major regulatory mechanism for cellular metabolism [i]. Another possible major regulatory mechanism may utilize allotopic interactions but this effect has not been extensively studied [2]. This paper reports our attempts to identify and study allotopic interactions of some mitochondrial NAD-linked dehydrogenases. The previous uncertainty about the localization of dehydrogenases within the mitochondrion has been clarified by recent work [3]. The inner membrane-matrix fraction of mitochondria retains most of the integrated functions which are characteristic of whole mitochondria. 3-Hydroxybutyrate dehydrogenase is bound very tightly to the inner mitochondrial membrane, whilst glutamate dehydrogenase and malate dehydrogenase are found ...

Semiquinone anion radicals formed by the reaction of quinones with glutathione or amino acids

“…The g value of 2.0047 is close to that calculated for the radical anion in a different solvent [15]. The radical anion of 5-OH-1,4-NQ displayed splitting constants of two doublets (0.319 and 0.699 G), one triplet (1.319 G) and two doublets whose splitting constants when summed were 6.30 G. Our spectrum appeared similar to that obtained by Dodd and Mukherjee [16] for this radical in aqueous media.…”

Rapid preparation of mitochondrial malate dehydrogenase from rat liver and heart

“…We have shown that subjecting enzyme from either source to a freeze-thaw cycle with lysolecithin abolished the multiplicity in both cases and converted both liver and heart enzyme to a single isoelectric form at pH 9.6. We have subsequently established, in agreement with Dodd (1973), that addition of lysolecithin stabilized the enzyme toward heart inactivation.…”

Cardiac mitochondrial alterations induced by insulin deficiency and hyperinsulinaemia in rats: Targeting membrane homeostasis with trimetazidine

“…The reduction of glutamate utilization in insulin‐deficient rats suggests a decrease in glutamate uptake by mitochondria or a decrease in glutamate dehydrogenase activity. Glutamate dehydrogenase has been linked to mitochondrial membrane PL, 37 especially to cardiolipin 38 . We hypothesized that insulin deficiency induced alterations of mitochondrial membrane fatty acids influence glutamate dehydrogenase activity and glutamate utilization.…”