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Biomedical subjects

R G Schneider

Publications and source records attributed to R G Schneider.

At least 19 recordsLinked to original sources
PubMed1984

Involvement of His HC3 (146) beta in the Bohr effect of human hemoglobin. Studies of native and N-ethylmaleimide-treated hemoglobin A and hemoglobin Cowtown (beta 146 His replaced by Leu).

The involvement of the COOH-terminal histidines of the beta chains of human hemoglobin in the allosteric mechanism of oxygen binding has been the topic of intensive discussion. Data presented here on the functional properties of native and chemically modified forms of Hb Cowtown (beta 146 His replaced by Leu) suggest that approximately half of the alkaline Bohr effect is attributable to the imidazole of His HC3(146) beta. The contribution of this residue to the alkaline Bohr effect has been estimated variably as 40-60% and 15% or less. Equilibrium and kinetic studies show that the amino acid substitution in Hb Cowtown decreases the stability of the low affinity conformation, resulting in an increased oxygen affinity and altered sensitivity to anionic effectors. Detailed analysis of Hill plots of oxygen binding according to the Adair scheme reveals that, under conditions of moderate ionic strength (chloride = 0.1 M), the K2 and K3 values for Hb A and Hb Cowtown differ, whereas the K1 and K4 values are closely similar over the physiological pH range. The decreased pH sensitivity of Hb Cowtown is associated with a decreased pH sensitivity of K1, the first Adair constant. In contrast to des-His(146 beta) hemoglobin, the cooperative interactions shown by Hb Cowtown under conditions of moderate ionic strength are not reduced in comparison to those of Hb A. This and the similarity of K1 and K4 values for Hb A and Hb Cowtown indicate that under these conditions the salt bridge formed by the COOH-terminal imidazole group does not significantly contribute to the free energy difference between "T-state" and "R-state" hemoglobin. It appears that the salt bridge formed by the COOH-terminal carboxyl group stabilizes the deoxy, T-state, conformation to a greater degree than previously appreciated. Chemical modification of the Cys(93 beta) residue of Hb Cowtown with N-ethylmaleimide causes a decrease in its oxygen affinity, in contrast to the increase in affinity exhibited by N-ethylmaleimide-modified Hb A. Hemoglobins A and Cowtown have remarkably similar oxygen binding properties after this modification and are shown to have K1 and K4 values distinctly different from those of unmodified Hb A. The properties of native and chemically modified forms of Hb Cowtown are indicative of a large contribution of the His HC3 (146) beta residue to the alkaline Bohr effect and also illustrate how chemical modifications or changes of strategic amino acid residues can result in pronounced differences in the conformational equilibrium of an allosteric protein.

Ethylmaleimide↗
PubMed1983

Hb S Mobile: a new genetic combination.

The genetic combination of Hb Mobile (beta 73 Asp replaced by Val) and Hb S (beta 6 Glu replaced by Val) was found in a healthy black man whose hemolysate resembles that of Hb S electrophoretically. His mother and sister have Hb AS; the father and brother have Hb A Mobile. No clinical nor hematologic abnormalities were detected in any member of the family. A slightly decreased oxygen affinity associated with Hb Mobile appears to have no clinical significance. Simple methods of differentiating Hb Mobile S from the electrophoretically similar but clinically severe Hb SD Los Angeles are described.

Adolescent↗
PubMed1980

HbE-beta-thalassemia associated with G6PD deficiency.

HbE, beta thalassemia, and G6PD deficiency were demonstrated in a 6-year-old Mexican-American child with anemia, jaundice, and delayed growth. The father was heterozygous for HbE, and the mother for beta-thalassemia and G6PD deficiency. The association of these three diseases should be included in the differential diagnosis of anemia in childhood, particularly after the recent influx of people form Southeast Asia into the United States.

Child↗
PubMed1980

Globin chain synthesis in haemoglobin New York (beta 113 replaced by glutamic acid).

The presence of Hb New York was confirmed in a Chinese family in which affected members have occasional red cells with Hb-H-like inclusions and a relative decrease in alpha chain synthesis, suggestive of a coexisting alpha thalassaemia trait. However, globin gene mapping and DNA hybridization revealed no deletion of the alpha genome. Timed-incubation experiments showed that the rate of synthesis of beta NY chain was greater than that of normal beta chain in the early periods. Chromatographic separation of Hb NY and Hb A before chain analysis revealed preferential binding of newly synthesized alpha chains to beta NY, with a four-fold increase in specific activity of the alpha Hb NY chains. It is concluded that beta NY chain is being synthesized more rapidly and its increased turnover may account for this presentation of apparent alpha chain deficiency.

Adult↗
PubMed1980

Biosynthesis of hemoglobin F Malta-I in culture by adult circulating erythropoietic precursors.

By using a methylcellulose clonal assay, we cultured peripheral blood erythropoietic precursors (BFU-E) from an adult couple whose child had HbF Malta-I(gamma 117 His leads to Arg), a G gamma variant, and measured the synthetic rates of HbA, HbF, and HbF Malta-I. Hemoglobin was labeled with 14C-amino acid in culture, separated by slab gel isoelectric focusing technique, and quantitated by autoradiographic or fluorographic method. Culture of BFU-E from both parents revealed significant HbF biosynthesis. HbF Malta-I was present in culture of the father's cells and comprised about 24% of total HbF. When we analyzed Hb biosynthesis in individual bursts, all bursts contained HbA and HbF in varying ratios. The frequency distribution of the individual bursts differing in percentages of HbF biosynthesis approached normal distribution. While the relative ratio of HbF Malta-I to total HbF biosynthesis in individual bursts also revealed significant variation, its frequency distribution did not show a normal distribution. There was a positive correlation between the ratios of HbF/Hb and HbF Malta-I/HbF in individual bursts.

Autoradiography↗
PubMed1980

Hemoglobin Ohio (beta 142 Ala replaced by): a new abnormal hemoglobin with high oxygen affinity and erythrocytosis.

Hemoglobin Ohio [beta 142 (H20) Ala replaced by Asp] was found in three members of a white family, all of whom showed erythrocytosis. The variant hemoglobin has a high oxygen affinity, a reduced Bohr effect, and diminished cooperativity. The functional abnormalities of Hb Ohio are explained by the proximity of the substituent beta 142 residue, both to beta 143 His, which is involved in the DPG binding site of hemoglobin, and to the critical C terminal region of the beta chain, which participates in the stabilization of the deoxy (T) conformation.

Adult↗
PubMed1979

Hemoglobin Cowtown (beta 146 HC3 His-Leu): a mutant with high oxygen affinity and erythrocytosis.

A new mutant, hemoglobin Cowtown, has been found in a white man and his father, both of whom have erythrocytosis. The father had previously been treated with 32P for polycythemia vera. The abnormal hemoglobin is not detectable on electrophoresis in alkaline buffers, but it resolves distinctively on electrophoresis in citrate agar, pH 6.0; similarly, the abnormal beta-globin chain does not separate from beta-A in urea 2-mercaptoethanol buffers of pH 8.9, but it moves anodically to beta-A at pH 6.0. Peptide chromatography and amino acid analysis of the beta chain reveal that the C-terminal histidine residue (beta 146) has been replaced by leucine. Like several other hemoglobins substituted at this residue, Hb Cowtown has a high oxygen affinity and a diminished Bohr effect.

Adult↗
PubMed1978

Hemoglobin Detroit: beta95 (FG2) lysine leads to asparagine.

Hb Detroit is a mutant which migrates between Hb A and Hb J Baltimore on cellulose acetate (pH 8.5), and with Hb A on citrate agar (pH 6.0). Globin chain analyses in alkaline and acid buffers reveal an abnormal beta chain with a mobility between the betaA and betaJ Baltimore chains. Structural characterization of this abnormal chain shows that lysine at position 95 is replaced by asparagine. No hematological abnormalities could be attributed to the presence of the mutant, and the oxygen affinity properties of the stripped hemoglobin are similar to those of Hb A. The beta95 residue which is substituted in Hb Detroit and also in Hb N Baltimore ((beta95 Lys leads to Glu) does not appear to be in a critical functional area of the molecule.

Adult↗
PubMed1978

Measuring relative electrophoretic mobilities of mutant hemoglobins and globin chains.

A system of calculating relative mobilities of mutant hemoglobins and globin chains in four methods of zone electrophoresis is described. In electrophoresis on cellulose acetate, TEB buffer, pH 8.5, mobilities are calculated as ratios of the mobility of simultaneously analyzed Hb C. In electrophoresis on citrate agar, pH 6.0, anodic mobilities are also related to Hb C, cathodic ones to Hb F. In globin electrophoresis in urea 2-mercaptoethanol buffers, pH 6.0 and 8.9, mobilities of the mutant globin chains are calculated in relation to the mobilities of normal alpha and beta chains. These calculations provide objective comparisons of mobilities of hemoglobins, including those analyzed at different times. The combined data permit recognition of many mutant hemoglobins.

Blood Protein Electrophoresis↗
PubMed1978

Methods for detection of hemoglobin variants and hemoglobinopathies in the routine clinical laboratory.

Many mutant hemoglobins and hemoglobinopathies can be identified with a high degree of specificity in the routine clinical laboratory. The most frequent abnormalities--those involving Hb S or C--are usually easily detectable in small amounts of sample analyzed by two simple methods of electrophoresis: cellulose acetate at pH 8.5 and citrate agar at pH 6. Some rarer mutants, e.g., Hb O, Hope, and Camden, can also be recognized by these two methods. Presumptive identification of other relatively frequent mutants, such as Hb D Los Angeles (Punjab) and Hb G Philadelphia, can be accomplished with additional data obtained from globin electrophoresis on cellulose acetate in acidic and alkaline buffers containing urea and 2-mercaptoethanol (or dithioerythritol). Electrophoretic profiles are presented of about a dozen hemoglobins likely to be encountered in screening programs in the U.S. Methods are also presented for identifying other genetic hemoglobin abnormalities--various types of thalassemia, Hb M, unstable hemoglobins, and those of the newborn.

Electrophoresis, Agar Gel↗