Oxidation of Reduced Nicotinamide Nucleotides in the Central Nervous System of some Marine Invertebrates

Abstract

INVESTIGATIONS carried out chiefly with mammalian brain have revealed the presence of several enzymatic systems catalysing the oxidation of reduced nicotinamide nucleotides the properties of which are briefly outlined as follows: (1) a mitochondrial system which catalyses the oxidation of NADH but not NADPH by oxygen the activity of which is inhibited by antimycin A and amytal¹ (NADH and NADPH stand respectively for the reduced forms of nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate); (2) two microsomal systems which catalyse respectively the oxidation of NADH and NADPH by cytochrome c and are not inhibited by these drugs¹; (3) two NAD(P)H dehydrogenases capable of acting on both nicotinamide nucleotides when certain quinones are added and which are strongly inhibited by low concentrations of dicumarol^2–4; (4) an NADH–ferricyanide reductase relatively insensitive to dicumarol⁵; (5) an NADPH–glutathione reductase⁶. The mitochondrial and the microsomal pathways are multi-component systems bound to these sub-cellular particles, while the remaining enzymes are soluble or readily solubilized proteins. With the exception of the mitochondrial NADH oxidase, which is known to be coupled to the process of oxidative phosphorylation, only scanty information is available on the part played by these oxidative systems. The complexity of mammalian brain presents additional difficulties in attempts to define the biological significance of these enzyme systems.