Previous studies of the Hpa I cleavage site-sickle cell hemoglobin gene linkage in various African populations suggested that the sickle gene arose independently more than once. In the present study we have performed restriction endonuclease haplotype analysis for the beta-globin-like gene cluster from four separate geographic areas in Africa, all of which possess the sickle gene. In Benin (Central West Africa) and Algeria (Arab North Africa) all chromosomes carrying the sickle gene possess an identical haplotype as defined by 11 different polymorphic restriction endonuclease sites within the 60-kilobase region of the beta-globin-like gene cluster. In the Central African Republic (Bantu-speaking Africa) and in Senegal (Atlantic West Africa) a very large proportion of the sickle gene chromosomes were associated with a haplotype specific for each country. Thus, three different haplotypes are shown to be associated with the sickle gene in Africa, and each is present at a very high frequency in geographically separate regions. Since the three haplotypes differ from each other by at least three sites residing both 5' and 3' to a putative hot spot for recombination, it is most likely that the sickle gene arose at least three times on separate preexisting chromosomal haplotypes. This may have implications for a better understanding of the variable nature of the expression of sickle cell anemia, because clinically relevant sequences (for example, gamma-globin gene regulatory sequences responsive to anemia) might be linked polymorphically to these haplotypes.
Patients with sickle cell anemia vary in the hematologic and clinical features of their disease, in part because of variability in the presence of linked and unlinked genes that modify the expression of the disease. The hemoglobin S gene is strongly linked to three different haplotypes of polymorphic endonuclease-restriction sites of the beta-like gene cluster (genes in the vicinity of the beta-globin gene)--one prevalent in Atlantic West Africa, another in central West Africa, and yet another in Bantu-speaking Africa (equatorial, East, and southern Africa). We have studied the differences in the hematologic characteristics of patients with sickle cell anemia from the first two geographical areas. We find that the Senegalese (Atlantic West Africa) patients have higher levels of hemoglobin F, a preponderance of G gamma chains in hemoglobin F, a lower proportion of very dense red cells, and a lower percentage of irreversibly sickled cells than those from Benin (central West Africa). We interpret these data to mean that the gamma-chain composition and the hemoglobin F level are haplotype linked and that the decrease in the percentage of dense cells and irreversibly sickled cells is secondary to the elevation in the hemoglobin F level. Patients with sickle cell anemia in the New World probably correspond to various combinations of these types, in addition to the still hematologically undefined haplotype associated with sickle cell anemia in the Bantu-speaking areas of Africa.
We have studied 42 homozygous 3-thalassemia patients from Algeria and 34 sickle cell anemia patients from Senegal and Benin, determinin* the relationship between haplotypes, Hb F, and G7yglobin/ -globin ratios. Populations selected have a high frequency of haplotype homozygotes because of consanguinity (Algeria) and geographic homogeneity (West Africa). We find in (-thalassemia In addition, haplotypes IX, m, and Senegalese sickle cell anemia patients exhibit hematological amelioration of their disease. Conversely, haplotypes I, V, and A in thalassemia pa-
One of the main difficulties with blood substitutes based on hemoglobin (Hb) solutions is the auto-oxidation of the hemes, a problem aggravated by the dimerization of Hb tetramers. We have employed a method to study the oxyHb tetramer-dimer equilibrium based on the rate of auto-oxidation as a function of protein concentration. The 16-fold difference in dimer and tetramer auto-oxidation rates (in 20 mM phosphate buffer at pH 7.0, 37 "C) was exploited to determine the fraction dimer. The results show a transition of the auto-oxidation rate from low to high protein concentrations, allowing the determination of the tetramer-dimer dissociation coefficient14-fold increase in K4,2 was observed for addition of 10 mM of the allosteric effector inositol hexaphosphate (IHP).Recombinant hemoglobins (rHb) were genetically engineered to obtain Hb with a lower oxygen affinity than native Hb (Hb A). The rHb a 9 2 [(C7) F41Y/(G4) N102Yl shows a fivefold increase in K4.2 at pH 7.0,37"C. An atmosphere of pure oxygen is necessary in this case to insure fully oxygenated Hb. When this condition is satisfied, this method provides an efficient technique to characterize both the tetramer-dimer equilibrium and the auto-oxidation rates of various oxyHb. For low oxygen affhity Hb equilibrated under air, the presence of deoxy subunits accelerates the auto-oxidation. Although a full analysis is complicated, the auto-oxidation studies for air equilibrated samples are more relevant to the development of a blood substitute based on Hb solutions. The double mutants, rHb a2p2 [(C7) F41Y/(G4) N102Al and rHb a2p2 [(C7) F41Y/(E10) K66T], show a lower oxygen afflnity and a higher rate of oxidation than Hb A. Simulations of the auto-oxidation rate versus Hb concentration indicate that very high protein concentrations are required to observe the tetramer auto-oxidation rate. Because the dimers oxidize much more rapidly, even a small fraction dimer will influence the observed oxidation rate.Keywords: auto-oxidation; hemoglobin; oxyhemoglobin; recombinant hemoglobin; tetramer-dimer equilibrium Despite the vast amount of research on hemoglobin (Hb), there are no rapid and reliable methods to measure the fraction of dimers. This is due to the difficulty of obtaining a reliable signal that differenciates between the dimeric and tetrameric species. Dimers have spectral and ligand binding properties similar to fully liganded tetramers. In addition, it is difficult to obtain data for pure dimers at pH 7, because one must use protein concentrations below 100 nM-a condition where the equilibria for the globin-heme (or hemin) and the monomerization may influence the results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.