Hemoglobin Gun Hill: deletion of five amino acid residues and impaired heme-globin binding

Unstable hemoglobins

About 70 variants of Hb A with associated hemolytic disorders have been reported during the past 30 years. I have classified them according to four grades of severity of chronic hemolysis. Acute episodes of severe hemolysis may be seen in all classes. In addition, some 80 variants without overt hemolysis have given positive results with in vitro hemoglobin instability tests. The stereochemical bases for instability can be conjectured in most cases, although few unstable hemoglobins have actually been studied by X-ray crystallography. The mechanisms for denaturation of normal Hb A and its acceleration in unstable hemoglobins were proposed some 15 years ago. The alterations of membrane lipids and proteins leading to red cell senescence and the relevance of hemoglobin denaturation to this process are presently being investigated. Several "hyperunstable" variants are clinically silent, or equivalent to a thalassemia, probably because of very efficient degradation of the abnormal chains.

A novel delta zero-thalassemia arising from a frameshift insertion, detected by direct sequencing of enzymatically amplified DNA

We describe a novel mutation in the delta globin gene of a compound heterozygote for delta o thalassemia and a deletion type G gamma + (A gamma delta beta) zero thalassemia. The delta was amplified using the polymerase chain reaction (PCR), and the amplified material was used in a direct sequencing experiment. The nucleotide sequence of the mutant delta gene showed that the insertion of an extra nucleotide at the third position of codon 91 in the second exon, which gives rise to a premature stop codon at position 94, leads to the silencing of this gene. The presence of the mutation in the carriers of delta-thalassemia in this family was confirmed by dot blot hybridization. A possible model for the insertion of the extra nucleotide is discussed.

Hyperunstable hemoglobin Koriyama anti-Hb Gun Hill insertion of five residues in the beta chain

A new hyperunstable hemoglobin was found in a Japanese girl who had very severe, chronic hemolytic anemia. Her parents and siblings were hematologically normal. The abnormal hemoglobin comprised a very small proportion of the total hemoglobin, although it was produced almost at the same rate as normal hemoglobin. Sequencing of an abnormal peptide which was liberated from the beta chain by hydrolysis with a protease from Staphylococcus aureus V8 disclosed the tandem insertion of a five-residue segment which included the proximal histidine at beta 92(F8).

Immunological evidence for an ornithine transcarbamylase lesion resulting in the formation of enzyme with smaller protein subunits

An unusual form of ornithine transcarbamylase deficiency was found in a male child who became unconscious at 8 months. Two maternal uncles had died during similar illnesses at 6 years and 11 years, respectively. Detailed studies of the enzyme showed 10% residual activity, a very low Km for carbamyl phosphate (0.015 mmol/l) and near normal amounts of immunoreactive protein with a smaller than normal subunit (molecular weight 37 800 instead of 39 700). This information was obtained from a 10 mg liver biopsy core using protein separation on SDS-polyacrylamide gel, electrophoretic transfer to nitrocellulose filters and probing with antibody to the enzyme. Resolution of the exact mutation causing this change will be of interest to those who are studying the processing of mitochondrial enzymes during transport from the cytoplasm.

Functional studies of abnormal hemoglobins in Japan

Oxygen binding properties of fifteen kinds of abnormal hemoglobins discovered in Japan were elucidated with the automatic oxygenation apparatus which was developed by Imai et al. This paper reviews the functional characteristics of those hemoglobins previously reported, presents functional data of some newly studied hemoglobins, and gives a discussion on structure-function relationships in those hemoglobins. This paper also describes a simple procedure for generating a predicted oxygen equilibrium curve of non-isolatable hemoglobin from equilibrium curves of normal hemolysate and hemolysate containing that hemoglobin.

Mathematical models for the evolution of multigene families by unequal crossing over

Mathematical models of homologous but unequal crossing over between sister chromatids are presented. For mispairing by one repeat, the evolution of a multigene family by unequal crossing over can be represented by a linear birth-death process. The fixation rate of one repeat in a multigene family is estimated. For mispairing by more than one repeat, some approximate results are obtained.

Some properties of hemoglobin Gun Hill

Hb Gun Hill has been found in an asymptomatic black female living in Alabama; neither her parents nor her two siblings carry the variant. The deletion of five amino acid residues in the beta chain of Hb Gun Hill (alpha2beta2 91-95 deleted) causes this variant to have a high oxygen affinity, an interaction coefficient of unity and an absence of the Bohr effect. The rate of oxidation of liganded Hb Gun Hill by the ferricyanide ion follows first-order kinetics. Hb Gun Hill is to a great extent dissociated into dimers over a wide range of pH values.

Altered erythropoiesis and increased hemolysis in hemoglobin M Akita (M Hyde Park beta92 His replaced by Tyr) disease

Hb M Akita disease is a cyanotic hemoglobinopathy found in Akita Prefecture, Japan. The abnormal hemoglobin was found to be the same as Hb M Hyde Park (beta92 His replaced by Tyr) by chemical analysis in 1967. In this disease signs of accelerated hemolysis (serum bilirubin, 2.4 mg/dl; splenomegaly, 2 finger breadths; Hb, 10.7 g/dl; reticulocyte index, 2.7) were noted, but the causes of its slight anemia were revealed to be fairly complex by ferrokinetic study, RBC life-span measurement, and 99mTc myeloscintigram. The anemia in this disease is caused not only by shortened erythrocyte survival (T 1/2 = 11.5 days by 51Cr-tagging method) and sequestration of red cells in the spleen (Spleen: liver ratio = 2.5 approximately 3.0 by 51Cr-surface counting), but also by slow supply of erythrocytes to the peripheral blood from the bone marrow, presumably, related to the existence of unstable Hb M Akita and its derivative (Hb Akita) in the erythroid cells. Both Carrell's isopropanol test and Heinz body formation test were positive. In spite of maximally increased total erythropoiesis (8 times as high as the normal level; M:E ratio = 0.22:1.0), supply of red cells from the bone marrow to the peripheral blood was significantly decreased. The distribution of hematopoietic sites throughout the body was reasonably uniform.

Dimethyl adipimidate: a new antisickling agent

A new approach to the prevention of sickling in vitro by use of the bifunctional crosslinking reagent, dimethyl adipimidate, is described. Prior treatment of sickle erythrocytes with dimethyl adipimidate will inhibit sickling in completely deoxygenated erythrocytes. Treated erythrocytes do not demonstrate the potassium loss and viscosity increase that usually accompany sickling. The oxygen affinity of hemoglobin in these cells is increased independently from changes in the concentration of 2,3-diphosphoglycerate. The hemoglobin obtained from treated erythrocytes contains a high-molecular-weight component as well as additional positively charged components. The relative degree to which chemical modification and/or crosslinking is an essential part of the antisickling properties of the material is not known.

Hemoglobin Grady: the first example of a variant with elongated chains due to an insertion of residues

A black 25-year-old woman and her father have a fast-moving alpha chain variant in an amount of 8% (the father) and 18% (the daughter). Structural data indicate that this chain has been elongated by the addition of three amino-acid residues to give the sequence: -Pro(114)-Ala(115)-Glu(116)-Phe(117)-Thr(118)-Glu-Phe-Thr-Pro(119)-Ala(120)-. The underlying genetic alteration responsible for hemoglobin Grady appears, therefore, to be a tandem duplication of nine base pairs which may have arisen by a process of mismatched intragenic crossing over. Functional and physicochemical properties of the variant are not greatly altered, and hematological data are normal.

Structural and functional studies on hemoglobin Bethesda (alpha2beta2 145His), a varient associated with compensatory erythrocytosis

Studies have been performed on a 12-yr-old Chinese girl with compensatory erythrocytosis due to the presence of hemoglobin Bethesda comprising about 45% of the red cell hemoglobin. Her parents and three siblings were normal. The oxygen affinity of her blood was markedly increased: under physiological conditions (pH 7.40, 37 degrees C). P(50) was 12.8 mm Hg (normal = 26.5 mm Hg). The red cell 2,3-diphosphoglycerate (2.3-DPG) level was normal. The abnormal hemoglobin could not be separated from hemoglobin A by zone electrophoresis at pH 8.6 or isoelectric focusing on polyacrylamide gel. However, after the hemoglobin was split into free alpha and beta chains by treatment with p-hydroxymercuribenzoate (PMB) or 6 M urea, an abnormal beta chain was readily demonstrated having a higher isoelectric point (more positive net charge) than normal beta(A). Structural analysis of the variant beta chain demonstrated the substitution of histidine for tyrosine at position 145: hemoglobin Bethesda (alpha(2)beta(2) (145His)). From earlier chemical and crystallographic studies, it has been postulated that this residue is a critical determinant of hemoglobin function. Hemoglobin Bethesda was separated from hemoglobin A by column chromatography. Oxygen equilibria of purified hemoglobin Bethesda revealed an extremely high oxygen affinity (exceeding that of isolated alpha and beta chains), and markedly reduced cooperativity. The Bohr effect of hemoglobin Bethesda was 1/3 that of hemoglobin A. However, hemoglobin Bethesda showed a significant interaction with 2.3-DPG and inositol hexaphosphate.

Synthesis of hemoglobin Gun Hill: increased synthesis of the heme-free beta-GH globin chain and subunit exchange with a free alpha-chain pool

Hemoglobin Gun Hill is an unstable mutant hemoglobin associated with mild compensated hemolysis. This abnormal protein has a deletion of five amino acids in the beta-chains. The deletion includes the heme-binding proximal histidine at position 92. The beta-chains of hemoglobin Gun Hill lack heme groups. Approximately 32% of the circulating hemoglobin in heterozygous subjects consists of the mutant hemoglobin. When reticulocytes were incubated with radioactive amino acid the specific activity of hemoglobin Gun Hill was three to six times that of hemoglobin A. Total incorporation of radioactivity into hemoglobin Gun Hill was two to three times that into hemoglobin A. There were 20-50% more total counts in beta-Gun Hill (beta(GH)) than in beta(A). These results indicate that in reticulocytes there was greater synthesis of the abnormal beta-chains than beta(A)-chains. The ratio of the specific activities of the alpha-chains of hemoglobin Gun Hill to the alpha-chains of hemoglobin A was 20: 1. There was evidence of a free pool of alpha-chains in the reticulocytes containing hemoglobin Gun Hill. After 10 min of incubation approximately 40% of the total alpha-chain radioactivity was in the free pool. When protein synthesis was blocked by incubation of reticulocytes with puromycin, the specific activity of the alpha-chains of hemoglobin Gun Hill continued to increase due to direct exchange of alpha-subunits between the free pool and preformed hemoglobin Gun Hill. Studies of the assembly of beta(A) and beta(GH) revealed that the rates of translation of the two polypeptide chains were equal and uniform. No evidence was obtained for the existence of "slow points" in the process of globin chain assembly. The studies also suggest that lack of strong heme-globin binding does not hinder the synthesis of globin chains.