Association of hemoglobin Saint Etienne (alpha2beta295F8 His replaced by G1n) with hemoglobins A and F. Synthesis and subunit exchange in vitro

Hb Auckland [alpha 87(F8) His-->Asn]: a new mutation of the proximal histidine identified by electrospray mass spectrometry

Hb Auckland is a newly described unstable hemoglobin with a mutation of alpha 97(F8)His-->Asn. This substitution, involving the proximal histidine, does not lead to methemoglobinemia, but to instability and accelerated heme loss. The clinical picture is of a mild compensated hemolytic anemia. The presence of an abnormal hemoglobin was first demonstrated by the isopropanol stability test and confirmed by electrospray ionization mass spectrometry of total lysate. This showed that 14% of the alpha chains had a mass of 15,103.4 Da, i.e. 23 Da less than normal. Examination of tryptic digests showed an identical decrease in mass for peptide alpha T-9 (from 2,997.4 to 2,974.5 Da). Subdigestion with endoproteinase Asp-N located the 23 Da loss to residues alpha 85-90, and further digestion with thermolysin identified the mutation as His-->Asn at position 87 of the alpha chain. This was confirmed by sequence analysis of the peptide alpha 85-90.

Hb Isehara (or Hb Redondo) [beta 92 (F8) His----Asn]: an unstable variant with a proximal histidine substitution at the heme contact

A 50-year-old Japanese female patient was found to have hemolytic anemia. Isoelectrofocusing of her hemolysate revealed two abnormal hemoglobin bands, one of which was very close to the Hb A2 band, and the other between the Hb A2 and Hb F bands. CM-cellulose column chromatography of the globin prepared from the abnormal hemoglobin showed that the abnormal chain eluted faster than the normal beta and delta chains; the beta X chain, however, did not separate from the normal beta chain in urea cellulose acetate electrophoresis. An instability test of the patient's hemolysate revealed the presence of an unstable component. Structural analysis of the abnormal beta chain indicated that the histidine residue at beta 92(F8) was replaced by an asparagine or aspartic acid residue. DNA amplified by polymerase chain reaction was sequenced by the dideoxy method. The nucleotide sequence of the beta 92 codon was AAC instead of CAC, suggesting that the amino acid substitution corresponded to His----Asn, which is the same as is found in Hb Redondo or beta 92(F8)His----Asn----Asp.

Genetic regulation of gamma gene expression: study of the interaction of beta-thalassemia with heterocellular HPFH

A family has been observed which a gene for heterocellular hereditary persistence of fetal hemoglobin (HPFH), probably identical to that previously described as Swiss type HPFH, has been inherited together with beta-thalassemia. The interaction of these two genes resulted in beta-thalassemia heterozygotes with unusually high levels of fetal hemoglobin (3.6-6.15), heterogeneously distributed. Globin synthesis studies showed a similar degree of chain imbalance in the heterocellular HPFH-beta thalassemia compound heterozygotes and in the heterozygous beta-thalassemia member of the family. On the basis of the pattern of genetic transmission of these two characters it can be concluded that the HPFH determinant does not behave as an allele of the gamma beta delta complex.

Globin-chain affinity chromatography on Sepharose-haptoglobin: a new method of study of hemoglobin synthesis in reticulocytes, in bone marrow and in colonies of erythroid precursors

In the present work we have developed an affinity chromatography system, using haptoglobin bound covalently to Sepharose 4B, to purify hemoglobin from soluble non-heme proteins. Sepharose-haptoglobin specifically binds hemoglobin. It exhibits the same characteristics in its interactions with hemoglobin and alpha or beta hemoglobin chains as does haptoglobin in solution. Globin chains can be eluted from the Sepharose-haptoglobin after removal of the heme. This method has allowed accurate measurements of globin-chain synthesis in blood and bone marrow samples and in culture of early erythroid precursors.

Elevated Hb F associated with beta-thalassaemia trait: haemoglobin synthesis in reticulocytes and in blood BFU-E

The red cells of a patient heterozygous for beta-thalassaemia contained 19% fetal Hb. Study of his family suggested that the proband had inherited the Swiss type of hereditary persistence of fetal Hb (HPFH) from his mother who is not thalassaemic and possessed 1.37% of Hb and 11% F-cells. Studies of globin synthesis showed a similar imbalance in the heterocellular HPFH-beta-thalassaemia compound heterozygotes and in the heterozygous beta-thalassaemic members of the family. Age stratification of the red cells showed a slight enrichment in Hb F and a decreased Hb A2 level in the older cell populations. Hb F production in the BFU-E colonies of the proband was higher than that found in vivo and in other beta-thalassaemic heterozygotes in culture. Study of single erythroid burst colonies showed a marked heterogeneity in Hb F synthesis from one colony to another, while the pool of free alpha-chains remained of similar magnitude. It is suggested that in the proband, the HPFH gene, which is in trans with respect to the beta-thal-gene, increases the size of the F-cell population and its activity is carried on at the expense of the normal beta A gene.

Fetal to adult hemoglobin switch in cultures of early erythroid precursors from human fetuses and neonates

Erythroid burst colonies derived from the cord blood of nine neonates and from the blood and liver of three fetuses aborted after 20 weeks of gestation were grown in plasma clot culture. Their quantitative study revealed a higher proportion of burst-forming units (BFU-Es) in cord blood than in cord blood of normal adults. In addition, colony-forming units (CFU-Es) were present in cord blood but absent from adult blood. Study of haemoglobin synthesis in 14-day cultures of cord blood BFU-Es showed a significantly higher degree of Hb A synthesis than was found in reticulocytes from fresh cord blood; this proportion was, however, similar to that expected in vivo about three weeks after birth. These data suggest that the hemoglobin switch is already programmed in most of the early erythroid precursors present in cord blood or full-term neonates and indicate that the differentiation time is probably of the same order of magnitude in vivo and in vitro. The proportion of Hb A and F synthesis in erythroid bursts was not influenced by the concentration of erythropoietin in the range studied--ie, from 0.5 to 12 international units. Low but identical proportions of Hb A synthesis were found both in erythroid cells from liver after two hours of incubation with [3H]-leucine, and in 14-day liver bursts from fetuses aborted at 20 weeks of gestation.

Hb Nottingham (alpha2beta2 (FG5) 98 val leads to gly) in a Caucasian male: clinical and biosynthetic studies

A second instance of the unstable mutant Hb Nottingham (alpha2beta2 (FG5) 98 Val leads to Gly) is reported in a 7-year-old boy. Because of splenomegaly, cholelithiasis, and frequent episodes of abdominal pain, he underwent a splenectomy and cholecystectomy at age 6. The surgery resulted in both an amelioration of his RBC destruction and an acceleration of his rate of growth.

Properties of the double substituted hemoglobin C Ziguinchor alpha2A beta 2 6 Glu replaced by Val 58 Pro replaced by Arg

We have previously described the structural identification of the sickle hemoglobin variant Hb C Ziguinchor (alpha2A beta2 6 Glu replaced by Val, 58 Pro replaced by Arg). This hemoglobin was found in two generations (three members) of an African family. In two family members, the clinical picture resembled that typical of a sickle cell trait, while the third member showed a more extreme clinical condition due to complication by an iron deficiency anemia. The functional properties of Hb C Zig. in red blood cells or in dilute solutions were identical to those of Hb S. The gelling behaviour of deoxy Hb C Zig. was also indistinguishable from that of Hb S. These findings suggest that, in contrast to the case of Hb C Harlem, the second substitution in position beta58 in Hb C Zig. does not interfere with the intermolecular interactions determined by the sickle substitution.