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Enzyme
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Target Concepts:
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Query: EC:1.6.99.3 (
diaphorase
)
5,903
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
There is increasing evidence that carbon monoxide (CO), like nitric oxide (NO), may be a neuronal messenger molecule. This study investigated the expression of
heme oxygenase-2
(
HO-2
), the enzyme responsible for the synthesis of CO, by intracardiac neurones. Many, if not all newborn guinea-pig intracardiac neurones in culture were
HO-2
-immunoreactive. Furthermore, double labelling showed that a relatively small subpopulation of these neurones also expressed NO synthase/nicotinamide dinucleotide phosphate (NADPH)-
diaphorase
(NOS/NADPH-d) activity. These findings suggest that intracardiac neurones can synthesize CO and that CO may be fundamental to their function. Comparison of the proportions of intracardiac neurones that contain
HO-2
with those that express NOS/NADPH-d activity also indicates that CO may be more important than NO in the intrinsic neuronal control of the heart.
...
PMID:Heme oxygenase-2 and nitric oxide synthase in guinea-pig intracardiac neurones. 914 Oct 89
It has recently been suggested that, in addition to nitric oxide (NO), carbon monoxide (CO) is an important gaseous messenger which might be involved in vertebrate olfactory transduction because its effects include activation of guanylyl cyclase and the formation of cGMP. As there is no information regarding the presence of
heme oxygenase-2
-- the constitutive isoform of the heme oxygenase system -- in olfactory neurons of non-rodent species, we have investigated the distribution pattern of
heme oxygenase-2
in the olfactory epithelium of the bovine, a representative of macrosmatics. Localization of nicotinamide adenine dinucleotide phosphate-
diaphorase
(NADPH-d) activity of the olfactory epithelium was compared with
heme oxygenase-2
and NO synthase (NOS) immunoreactivities in order to obtain possible hints at functional significance. NADPH-d activity was particularly intense in apical dendrites of receptor neurons. It was also found in Bowman glands and intraepithelial duct cells. Less intense, discrete NADPH-d activity was present also at intermediate and basal levels of the olfactory epithelium, corresponding to the layer of receptor neuron somata and basal cells. While
heme oxygenase-2
activity mainly occurred in neuronal perikarya, a very intense NOS immunoreactivity, exclusively for the inducible isoform, was detected in the apical dendrites. Ultrastructurally, NADPH-d histochemistry showed distinct labelling of membranes, in particular of endoplasmic reticulum, mitochondria and nucleus. The coincident localization of the moderate NADPH-d activity and
heme oxygenase-2
immunoreactivity in receptor cell perikarya suggest a functional association between NADPH-cytochrome P450 reductase and
heme oxygenase-2
. In contrast, dendritic localization of NADPH-d activity is topically and possibly functionally related to the presence of the inducible isoform of NOS. The results suggest that both CO and NO may be generated in bovine receptor neurons and thus involved in odorant stimulation. Based on immunocytochemical localization of synthesizing enzymes, NO might be regarded as a direct regulator of transduction related processes while CO might act as a modulator of the initial signal.
...
PMID:Heme oxygenase-2 and nitric oxide synthase immunoreactivity of bovine olfactory receptor neurons and a comparison with the distribution of NADPH-diaphorase staining. 1094 53
Hypoxia resulting from reduced oxygen (O
2
) levels in the arterial blood is sensed by the carotid body (CB) and triggers reflex stimulation of breathing and blood pressure to maintain homeostasis. Studies in the past five years provided novel insights into the roles of
heme oxygenase-2
(
HO-2
), a carbon monoxide (CO)-producing enzyme, and
NADH dehydrogenase
Fe-S protein 2, a subunit of the mitochondrial complex I, in hypoxic sensing by the CB.
HO-2
is expressed in type I cells, the primary O2-sensing cells of the CB, and binds to O
2
with low affinity. O
2
-dependent CO production from
HO-2
mediates hypoxic response of the CB by regulating H
2
S generation. Mice lacking NDUFS2 show that complex I-generated reactive oxygen species acting on K
+
channels confer type I cell response to hypoxia. Whether these signaling pathways operate synergistically or independently remains to be studied.
...
PMID:Recent advances in understanding the physiology of hypoxic sensing by the carotid body. 3063 32
