Thrombopoietin in normal and neoplastic stem cell development.

It has been known for sometime that thrombopoietin acts on megakaryocytic progenitor cells to stimulate platelet production. It has recently been discovered that it also stimulates the self-renewal and expansion of normal murine and human haematopoietic stem cells (HSCs) by acting on its cognate receptor, the product of the myeloproliferative leukaemia (c-MPL) proto-oncogene. The c-MPL receptor may also play an important role in the development of human myeloproliferative disorders, essential thrombocythemia, myelofibrosis and polycythemia vera, cooperating with the dysregulated Janus kinase JAK2V(617)F.

Some properties of hemoglobin A2.

While no significant physiologic function of hemoglobin A2 (Hb A2), the minor basic component of human hemoglobin, has been recognized, only its oxygen equilibria have been studied in detail. Since hemoglobin A2 and its oxidative denaturation product, hemichrome A2, bind to the red cell membrane, particularly to band 3, to a greater extent than do Hb A or hemichrome A, some of the properties of Hb A2 that might influence hemoglobin-membrane association were examined. Hemoglobin A2 exhibited slightly increased susceptibility to autoxidation to methemoglobin.

Growth of Plasmodium falciparum in human erythrocytes containing abnormal membrane proteins.

To evaluate the role of erythrocyte (RBC) membrane proteins in the invasion and maturation of Plasmodium falciparum, we have studied, in culture, abnormal RBCs containing quantitative or qualitative membrane protein defects. These defects included hereditary spherocytosis (HS) due to decreases in the content of spectrin [HS(Sp+)], hereditary elliptocytosis (HE) due to protein 4.1 deficiency [HE(4.

Frequencies of Band 3 variants of human red cell membranes in some different populations.

A variant of Band 3, the major protein of the erythrocyte membrane, was observed by Mueller and Morrison in 1977 in 6-7% of healthy blood donors on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of erythrocyte membranes treated with pronase. Pronase treated red cells containing this first recognized variant [here designated 'Band 3-Memphis (m)'] section had two bands of about 63,000 and 60,000 Mr while pronase treated normal cells had only the lighter Mr band. The present study includes data on the frequency of variants resembling Band 3-Memphis in patients of different ethnic groups and on random donors obtained earlier in Memphis.

Reverse phase high-performance liquid chromatography and secondary ion mass spectrometry. A strategy for identification of ten human hemoglobin variants.

Ten abnormal hemoglobins were detected and characterized in individual cases referred to our laboratory for evaluation of hematological problems. Six of these variants were electrophoretically silent and could be detected by reverse phase high-performance liquid chromatography (HPLC) analysis. HPLC was also used to analyze the tryptic peptides of each individual variant.

Some properties of hemoglobin mobile (alpha 2 beta 2 73 Asp----Val).

A hemoglobin variant was identified as hemoglobin Mobile in which valine replaces the normal aspartic acid at beta 73. Studies of its oxygen equilibria and of its interactions in gelation when mixed with hemoglobin S were carried out. Hemoglobin Mobile had an oxygen affinity lower than that of hemoglobin A, as observed by others.

Association of hemoglobin C with erythrocyte ghosts.

The interaction of hemoglobin C (Hb C) with erythrocyte membranes was studied using changes in fluorescence intensity in a membrane-embedded probe. The affinity of Hb C for the membranes at pH 6.0 and pH 6.

Interactions of hemoglobin S with the red cell membrane.

Significant differences were observed in the binding of hemoglobin A and hemoglobin S to normal red cell membranes containing the fluorescent chromophore 12-(9-anthroyl) stearic acid. Deoxyhemoglobin S had a greater affinity for the membrane than did deoxyhemoglobin A and part of the binding of deoxyhemoglobin S appeared to be irreversible. When the hemoglobin binding site in red cell membranes, Band 3, was blocked with with glyceraldehyde-3-phosphate dehydrogenase, neither hemoglobin S nor A was bound.

Interaction of sickle cell hemoglobin with erythrocyte membranes.

The interactions of hemoglobin S with the erythrocyte membrane were compared with the corresponding interactions of hemoglobin A by measuring in both steady-state and kinetic experiments the quenching of the fluorescence of a probe embedded in erythrocyte membranes. Whereas hemoglobin A could be dissociated from membranes, a fraction of hemoglobin S was irreversibly bound even in the oxy state. Deoxyhemoglobin S interacted much more strongly with erythrocyte membranes than did deoxyhemoglobin A: a portion of the deoxyhemoglobin S was irreversibly bound, and the reversibly bound fraction of hemoglobin S dissociated more slowly than did deoxyhemoglobin A.

Kinetics of ligation reactions of rabbit hemoglobin in quaternary R and T states.

Rabbit hemoglobin shows significantly lower affinity for CO than does human hemoglobin (Hb A). The overall ligand combination and dissociation rate constants reveal, however, only small differences between Hb A rabbit Hb; this is mainly due to the fact that beta chains in rabbit hemoglobin determine the kinetics of ligand dissociation and combination. The heme environment in these chains is probably not very different in rabbit Hb and human Hb A.

Bimane fluorescent labels. Characterization of the bimane labeling of human hemoglobin.

The products of the bimane labeling (using a monobromobimane, a dibromobimane and a quaternary bromobimane) of hemoglobin are characterized. Peptide mapping identifies cysteine-beta 93 as the reactive thiol site. Electrophoretic mobility of hemoglobin varies with the label used, that of monobromobimane-labeled hemoglobin being unaltered, while dibromobimane- and trimethylammoniobromobimane-labeled hemoglobin exhibit changes.