Role of Heme Distortion on Oxygen Affinity in Heme Proteins: The Protoglobin Case

In this work, initial crystallographic studies of human haemoglobin (Hb) crystallized in isoionic and oxygen-free PEG solution are presented. Under these conditions, functional measurements of the O2-linked binding of water molecules and release of protons have evidenced that Hb assumes an unforeseen new allosteric conformation. The determination of the high-resolution structure of the crystal of human deoxy-Hb fully stripped of anions may provide a structural explanation for the role of anions in the allosteric properties of Hb and, particularly, for the influence of chloride on the Bohr effect, the mechanism by which Hb oxygen affinity is regulated by pH. X-ray diffraction data were collected to 1.87 Å resolution using a synchrotron-radiation source. Crystals belong to the space group P21212 and preliminary analysis revealed the presence of one tetramer in the asymmetric unit. The structure is currently being refined using maximum-likelihood protocols.

Download Full-text

Red cell oxygen affinity in fetal sheep: role of 2,3-DPG and adult hemoglobin

Journal of Applied Physiology ◽

10.1152/jappl.1978.45.1.7 ◽

1978 ◽

Vol 45 (1) ◽

pp. 7-10 ◽

Cited By ~ 5

Author(s):

H. Bard ◽

J. C. Fouron ◽

J. E. Robillard ◽

A. Cornet ◽

M. A. Soukini

Keyword(s):

Red Blood Cells ◽

Blood Cells ◽

Oxygen Affinity ◽

Fetal Life ◽

Red Cell ◽

Adult Type ◽

Fetal Sheep ◽

Adult Hemoglobin ◽

Relationship Of

Studies were carried out during fetal life in sheep to determine the relationship of 2,3-diphosphoglycerate (DPG), the intracellular red cell and extracellular pH, and the switchover to adult hemoglobin synthesis in regulating the position of the fetal red cell oxygen-affinity curve in utero. Adult hemoglobin first appeared near 120 days of gestation. The mean oxygen tension at which hemoglobin is half saturated (P50) prior to 120 days of gestation remained constant at 13.9 +/- 0.3 (SD) Torr and then increased gradually as gestation continued, reaching 19 Torr at term. During the interval of fetal life studied, the level of DPG was 4.43 +/- 1.63 (SD) micromol/g Hb and the deltapH between plasma and red blood cells was 0.227 +/- 0.038 (SD); neither was affected by gestational age. The decrease in the red cell oxygen affinity after 120 days of gestation ocrrelated with the amount of adult hemoglobin present in the fetus (r = 0.78; P less than 0.001). This decrease can be attributed only to the amount of the adult-type hemoglobin present, and not to DPG, or to changes in the deltapH between plasma and red blood cells, because both remained stable during the last trimester.

Download Full-text

Novel Reiterated Fnr-Type Proteins Control the Production of the Symbiotic Terminal Oxidase cbb3 in Rhizobium etli CFN42

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-20-10-1241 ◽

2007 ◽

Vol 20 (10) ◽

pp. 1241-1249 ◽

Cited By ~ 15

Author(s):

Manuel J. Granados-Baeza ◽

Nicolás Gómez-Hernández ◽

Yolanda Mora ◽

María J. Delgado ◽

David Romero ◽

...

Keyword(s):

Nitrogen Fixation ◽

Oxygen Affinity ◽

Structural Similarity ◽

Transcriptional Regulators ◽

Terminal Oxidase ◽

Nitrogen Fixing ◽

Rhizobium Etli ◽

High Oxygen Affinity ◽

Key Genes

Symbiotic nitrogen-fixing bacteria express a terminal oxidase with a high oxygen affinity, the cbb3-type oxidase encoded by the fixNOQP operon. Previously, we have shown that, in Rhizobium etli CFN42, the repeated fixNOQP operons (fixNOQPd and fixNOQPf) have a differential role in nitrogen fixation. Only the fixNOQPd operon is required for the establishment of an effective symbiosis; microaerobic induction of this operon is under the control of at least three transcriptional regulators, FixKf, FnrNd, and FnrNchr, belonging to the Crp/Fnr family. In this work, we describe two novel Crp/Fnr-type transcriptional regulators (StoRd and StoRf, symbiotic terminal oxidase regulators) that play differential roles in the control of key genes for nitrogen fixation. Mutations either in stoRd or stoRf enhance the microaerobic expression of both fixNOQP reiterations, increasing also the synthesis of the cbb3-type oxidase in nodules. Despite their structural similarity, a differential role of these genes was also revealed, since a mutation in stoRd but not in stoRf enhanced both the expression of fixKf and the nitrogen-fixing capacity of R. etli CFN42.

Download Full-text

NTP pattern of avian embryonic red cells: role of RNA degradation and AMP deaminase/5′-nucleotidase activity

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00461.2002 ◽

2003 ◽

Vol 284 (3) ◽

pp. R771-R779 ◽

Cited By ~ 5

Author(s):

Rosemarie Baumann ◽

Robert Götz ◽

Stefanie Dragon

Keyword(s):

Hormonal Regulation ◽

Oxygen Affinity ◽

Erythroid Differentiation ◽

Rna Degradation ◽

Amp Deaminase ◽

Key Enzymes ◽

Allosteric Effectors ◽

Hemoglobin Oxygen Affinity ◽

Adult Hemoglobin

During terminal erythroid differentiation, degradation of RNA is a potential source for nucleotide triphosphates (NTPs) that act as allosteric effectors of hemoglobin. In this investigation, we assessed the developmental profile of RNA and purine/pyrimidine trinucleotides in circulating embryonic chick red blood cells (RBC). Extensive changes of the NTP pattern are observed which differ significantly from what is observed for adult RBC. The biochemical mechanisms have not been identified yet. Therefore, we studied the role of AMP deaminase and IMP/GMP 5′-nucleotidase, which are key enzymes for the regulation of the purine nucleotide pool. Finally, we tested the effect of major NTPs on the oxygen affinity of embryonic/adult hemoglobin. The results are as follows. 1) Together with ATP, UTP and CTP serve as allosteric effectors of hemoglobin. 2) Degradation of erythroid RNA is apparently a major source for NTPs. 3) Developmental changes of nucleotide content depend on the activities of key enzymes (AMP deaminase, IMP/GMP 5′-nucleotidase, and pyrimidine 5′-nucleotidase). 4) Oxygen-dependent hormonal regulation of AMP deaminase adjusts the red cell ATP concentration and therefore the hemoglobin oxygen affinity.

Download Full-text