The Effects of
Hyperoxia, Hypoxia, and Ischemia/Reperfusion on
the Activity of Cytochrome Oxidase from the Rat
Retina
A. ŠIŠKOVÁ, J.
WILHELM
Department of
Medical Chemistry and Biochemistry, Second
Medical School, Charles University, Prague, Czech
Republic
Received
August 1, 2000
Accepted October 27, 2000
Summary
Cytochrome
oxidase activity from the retina can be enhanced
or depressed by free radical-mediated reactions
both in positive and negative aspect. The
greatest effect was exerted by
ischemia/reperfusion, which significantly
increased the fluorescent products of lipid
peroxidation (358 %, P<0.01) and inhibited the
enzyme activity (14 %, P<0.001). After
hyperoxia the fluorescent products slightly
increased (192 %, P< 0.05) as well as the
enzyme activity (133 %, P<0.05). Hypoxia had
no effect on any of these parameters. Specific
changes in the composition of fluorophores after
ischemia/reperfusion were revealed in the
fluorescence spectra. The fact that increased
lipid peroxidation after hyperoxia and after
ischemia/reperfusion does not produce the same
effect upon cytochrome oxidase activity might be
explained by changes in the kinetic behavior of
cytochrome oxidase. In the control enzyme
preparation, two binding sites for cytochrome c
were observed. One was of the low-affinity (Km=60
mM) and the other of the high-affinity (Km=1.12
mM). After in vitro-initiated lipid peroxidation,
the low-affinity binding site was lost and the
activity measured under "optimum"
conditions at a single cytochrome concentration
was higher than in the controls. This implies
that oxidative damage to cytochrome oxidase in
vivo can be site-specific and its extent should
be estimated by performing detailed kinetic
analysis as otherwise the results might be
misleading.
Key
words
Cytochrome
oxidase · Retina · Hypoxia · Hyperoxia ·
Ischemia/reperfusion · Lipid peroxidation
Reprint
requests
Dr.
J. Wilhelm, Department of Medical Chemistry and
Biochemistry, Second Faculty of Medicine, Charles
University, Plzeňská 221, 150 00 Praha 5, Czech
Republic, e-mail: jiri.wilhelm@lfmotol.cuni.cz
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