Aqua-photic Respiratory Cycle

An interpretive view of a seemingly useless vestigial human trait, affecting 1/3 of Europeans (and other people), is here hypothesized as having been a formerly significant part of the respiratory cycle in ancient human ancestors.
Author: David Deden

The following are different scientific articles on oxygen use and conservation in regards to physiology. Nitric Oxide (NO), Iron (Fe), Globins (Neuro- Cyto- Hemo- Myo-), L-DOPA, and other chemicals are involved in O2 transport and use in the body. During cool temperatures and during apnea (breath holding), certain Oxygen conservation patterns occur throughout the body, especially in the brain and eyes (which are heavy users of O2).

Neuroglobin (Ngb), a globular heme protein expressed in the brain of vertebrates, binds oxygen reversibly, with an affinity comparable to myoglobin (Mb). Despite low sequence identity, the overall 3D fold of Ngb and Mb is very similar. Unlike in Mb, in Ngb the sixth coordination position of the heme iron is occupied by the distal histidine, in the absence of an exogenous ligand. Endogenous ligation has been proposed as a unique mechanism for affinity regulation and ligand discrimination in heme proteins. This peculiarity might be related to the still-unknown physiological function of Ngb. Here, we present the x-ray structure of CO-bound ferrous murine Ngb at 1.7 Å and a comparison with the 1.5-Å structure of ferric bis-histidine Ngb.

A vertebrate globin expressed in the brain. [Nature]
Burmester T, Weich B, Reinhardt S, Hankeln T. Institute of Zoology, Johannes Gutenberg University Mainz, Germany.

Haemoglobins and myoglobins constitute related protein families that function in oxygen transport and storage in humans and other vertebrates. Here we report the identification of a third globin type in man and mouse. This protein is predominantly expressed in the brain, and therefore we have called it neuroglobin. Mouse neuroglobin is a monomer with a high oxygen affinity (half saturation pressure, P50 approximately 2 torr). Analogous to myoglobin, neuroglobin may increase the availability of oxygen to brain tissue. The human neuroglobin gene (NGB), located on chromosome 14q24, has a unique exon-intron structure. Neuroglobin represents a distinct protein family that diverged early in metazoan evolution, probably before the Protostomia/Deuterostomia split.

Neuroglobin and cytoglobin. Fresh blood for the vertebrate globin family.
Pesce A, Bolognesi M, Bocedi A, Ascenzi P, Dewilde S, Moens L, Hankeln T, Burmester T.
Department of Physics-INFM and Center for Excellence in Biomedical
Research, University of Genova, Via Dodecaneso 33, I-16146 Genova, Italy.

Neuroglobin and the survival of the neuron
Martino Bolognesi

After cardiovascular disease and cancer, stroke and other hypoxia-related diseases are the third most common causes of death in many industrialised countries. In Europe, they represent the most important cause of morbidity and long-term disability imposing an enormous economic burden.The brain/s response to hypoxia and ischemia, which helps determine the clinical outcome, is a complex pattern of events including the synthesis of neuroprotective proteins. These proteins will help to counteract the adverse effects of hypoxia or ischemia by increasing anaerobic metabolism, tissue vascularity and
02 delivery or by the elimination of toxic compounds. Neuroglobin is an 02-binding protein suggested to enhance the 02 supply of the brain. We propose to study neuroglobin in normal and pathologic conditions in order to elucidate its role in the survival of the neuron under hypoxic and ischemic conditions. Neuroglobin and cytoglobin are two recently discovered members of the vertebrate globin family. Both are intracellular proteins endowed with hexacoordinated heme-Fe atoms, in their ferrous and ferric forms, and display O2 affinities comparable with that of myoglobin. Neuroglobin, which is predominantly expressed in nerve cells, is thought to protect neurons from hypoxic-ischemic injury. It is of ancient evolutionary origin, and is homologous to nerve globins of invertebrates.
Cytoglobin is expressed in many different tissues, although at varying levels. It shares common ancestry with myoglobin, and can be traced to early vertebrate evolution. The physiological roles of neuroglobin and cytoglobin are not completely understood. Although supplying cells with O2 is the likely function, it is also possible that both globins act as O2-consuming enzymes or as O2 sensors. Here, we review what is currently known about neuroglobin and cytoglobin in terms of their function, tissue distribution and relatedness to the well-known hemoglobin and myoglobin. Strikingly, the data reveal that O2 metabolism in cells is more complicated than was thought before, requiring unexpected O2-binding proteins with potentially novel functional features.

Neuroglobin, nitric oxide, and oxygen: Functional pathways and conformational changes
Maurizio Brunori *,Alessandro Giuffrè *, Karin Nienhaus G. Ulrich Nienhaus §, Francesca Maria Scandurra * and Beatrice Vallone **Department of Biochemical Sciences and Consiglio Nazionale delle Ricerche Institute of Molecular Biology and Pathology, University of Rome "La Sapienza," 00185 Rome, Italy; Department of Biophysics, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany; and §Department of Physics, University of Illinois, 1110 West Green Street, Urbana, IL 61801. Edited by Britton Chance, University of Pennsylvania School of Medicine, Philadelphia, PA and approved April 21, 2005 (received for review November 24, 2004)

Neuroglobin (Ngb) is a globin expressed in the nervous system of humans and other organisms that is involved in the protection of the brain from ischemic damage. Despite considerable interest, however, the in vivo function of Ngb is still a conundrum. In this paper we report a number of kinetic experiments with O2 and NO that we have interpreted on the basis of the 3D structure of Ngb, now available for human and murine metNgb and murine NgbCO.

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