INHIBITION BY REDUCED NICOTINAMIDE-ADENINE DIINUCLEOTIDE OF RAT LIVER XANTHINE OXIDASE TYPE D AND OF CHICK LIVER XANTHINE DEHYDROGENASE By E. DELLA CORTE AND F. STIRPE
نویسندگان
چکیده
The oxidation of hypoxanthine to xanthine and of xanthine to uric acid is catalysed by xanthine oxidase (EC 1.2.3.2). This enzyme has been considered to be an oxidase in mammalian organs (De Renzo, 1956), whereas it is a dehydrogenase in the organs of birds, with NAD+ probably being the physiological electron acceptor (Morell, 1955a,b; Fellig & Wiley, 1958). We have reported that in freshly prepared supernatant from rat liver the conversion of xanthine into uric acid occurs only to a limited extent through an oxidase reaction, and about five times as rapidly through a NAD+dependent dehydrogenation. The rate of the dehydrogenase reaction decreased and that of the oxidase increased if the supernatant was submitted to a variety of treatments, such as keeping it at -20°C for some hours (Della Corte & Stirpe, 1968a), preincubating it with proteolytic enzymes (Della Corte & Stirpe, 1968b) or with any particulate subcellular fraction, or keeping it under anaerobic conditions (Stirpe & Della Corte, 1969). The effects of proteolytic enzymes and of anaerobiosis were accelerated by the presence of xanthine. Similar observations were made with human liver (Della Corte, Gozzetti, Novello & Stirpe, 1969), whereas in all other rat organs examined the reaction appeared to be entirely an oxidase (Stirpe & Della Corte, 1969). On the basis of these results, it was postulated that in the liver of rat and man, and presumably of other mammals, the xanthine 'oxidase' may exist in two interconvertible forms: an oxidase, type 0, and a dehydrogenase, type D. The fact that in one case at least the conversion of typeD into type 0 is reversible allows one to suppose that the interconversion between the two types may occur under physiological conditions, and may possibly play a role in the regulation of xanthine oxidase activity. We report in this paper that the xanthine oxidase
منابع مشابه
The regulation of rat liver xanthine oxidase. Conversion in vitro of the enzyme activity from dehydrogenase (type D) to oxidase (type O).
متن کامل
Liver Xanthine Oxidase INVOLVEMENT OF THIOL GROUPS IN THE CONVERSION OF THE ENZYME ACTIVITY FROM DEHYDROGENASE (TYPE D) INTO OXIDASE (TYPE 0) AND PURIFICATION OF THE ENZYME By E. DELLA CORTE and F. STIRPE
1. The 'xanthine oxidase' activity of rat liver supernatant, most of which behaves as an NAD+-dependent dehydrogenase (type D) can be rapidly converted into an oxidase (type 0) by thiol reagents such as tetraethylthiuram disulphide, copper sulphate, 5,5'-dithiobis(2-nitrobenzoic acid), N-ethylmaleimide and p-hydroxymercuribenzoate. Treatment with copper sulphate, if prolonged, leads to almost c...
متن کاملIschaemic myelopathy associated with cocaine: clinical, neurophysiological, and neuroradiological features.
Two patients with spinal infarction and one patient with the previously unreported complication of spinal transient ischaemic attack associated with cocaine misuse are reported. Spinal MRI documented an infarction in the territory of the anterior spinal artery in the first two patients and was completely normal in the patient with a transient ischaemic attack. Motor evoked potentials were abnor...
متن کاملThe Mini-Sigh Test: A New Haemodynamic Test of Fluid Responsiveness in Icu Patients Undergoing Pressure Support Ventilation
Introduction Dynamic predictors of fluid responsiveness (FR) perform poorly in ICU patients receiving partial ventilatory assistance. Because these modes of partial support are increasingly used, FR dynamic indexes are applicable only in a few ICU patients [1]. To overcome these limitations, novel approaches for testing FR in ICU have been proposed, such as the passive leg raising and the end-e...
متن کاملThe Castalia mission to Main Belt Comet 133P/Elst-Pizarro
We describe Castalia, a proposed mission to rendezvous with a Main Belt Comet (MBC), 133P/Elst-Pizarro. MBCs are a recently discovered population of apparently icy bodies within the main asteroid belt between Mars and Jupiter, which may represent the remnants of the population which supplied the early Earth with water. Castalia will perform the first exploration of this population by characteri...
متن کامل