The triplet lifetime and absorption anisotropy decay of eosin-labeled band 3 was measured in resealed erythrocyte ghosts. Membrane potentials were generated by the addition of valinomycin in the presence of a K+ gradient. Neither negative nor positive membrane potentials had any detectable effect on the rotational diffusion of band 3 nor on the eosin triplet lifetime. The membrane potential did, however, affect quenching of the eosin triplet state by I- and TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl). Quenching was enhanced by a negative membrane potential (negative inside) and reduced by a positive membrane potential. In addition, it was found that a negative membrane potential enhanced the efficiency of eosin labeling of band 3 in intact erythrocytes. A positive membrane potential had the opposite effect. These results indicate that the eosin binding site on band 3 becomes more accessible to the extracellular aqueous phase in the presence of a negative membrane potential and less accessible in the presence of a positive membrane potential. Quenching by I- and TEMPO of the triplet state of eosin-labeled band 3 was further investigated as a function of pH. Quenching by TEMPO and its dependence on membrane potential were relatively insensitive to pH. In contrast, the rate of quenching by I- showed a marked decrease over the range pH 5.5-9.5. Moreover, the effect of a negative membrane potential on I- quenching also varied with pH. These results are discussed on the supposition that the eosin probe is located in the anion access channel of band 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Anion Exchange Protein 1, Erythrocyte↗

PubMed1992

Both ankyrin and band 4.1 are required to restrict the rotational mobility of band 3 in the human erythrocyte membrane.

A population of band 3 proteins in the human erythrocyte membrane is known to have restricted rotational mobility due to interaction with cytoskeletal proteins. We have further investigated the cause of this restriction by measuring the effects on band 3 rotational mobility of rebinding ankyrin and band 4.1 to ghosts stripped of these proteins as well as spectrin and actin. Rebinding either ankyrin or 4.1 alone has no detectable effect on band 3 mobility. Rebinding both these proteins together does, however, reimpose a restriction on band 3 rotation. The effect on band 3 rotational mobility of rebinding ankyrin and 4.1 are similar irrespective of whether or not band 4.2 is removed from the membrane. We suggest that ankyrin and 4.1 together promote the formation of slowly rotating clusters of band 3.

Anion Exchange Protein 1, Erythrocyte↗

PubMed1990

Transient dichroism studies of spectrin rotational diffusion in solution and bound to erythrocyte membranes.

Spectrin was purified from human erythrocytes and labeled with the triplet probe eosin-5-maleimide. Rotational diffusion of spectrin was investigated by observing transient dichroism following flash excitation of the probe. Measurements were performed at 4 degrees C in solutions of varying viscosity and with spectrin rebound to spectrin/actin-depleted erythrocyte membranes. In solution, complex anisotropy decays were observed which could not be satisfactorily fitted by the equations for a rod-shaped molecule of appropriate dimensions. When spectrin was rebound to the erythrocyte membrane, a decay in the anisotropy was still present but was markedly less sensitive to solution viscosity and flatter at longer times. In order to overcome the objection that the cytoskeleton is only partially reconstituted when spectrin is rebound, a method was developed for labeling spectrin with eosin-5-maleimide in situ. Anisotropy decays for these labeled membranes exhibited features similar to those obtained for spectrin labeled in solution and subsequently rebound. Taken together, the results provide good evidence for segmental motion of spectrin when incorporated into the erythrocyte cytoskeleton. Upon increasing the temperature, the initial anisotropy ro for both rebound and in situ labeled spectrin decreases, and above 30 degrees C the measured anisotropies are small. Thus, at physiological temperature the probe is almost completely randomized by motions with correlation times less than 10 microseconds.

Circular Dichroism↗

PubMed1990

Interaction of erythrocyte cytoskeletal proteins with band 3: rotational diffusion measurements.

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Actins↗

PubMed1987

A second Australian family with hemoglobin North Shore (beta 134 Val----Glu).

A second Australian family is reported with Hemoglobin North Shore (beta 134 Val----Glu), an unstable hemoglobin, causing no clinical symptoms. All affected family members showed only mild reticulocytosis and microcytosis on the blood film, despite the strongly positive isopropanol test for Hb (hemoglobin) stability and numerous red cell inclusions. Hb North Shore constituted 31-38% of the total hemoglobin and migrated on the anodal side of Hb A at pH 8.9. The association of a mildly raised Hb A2 level and thalassemic phenotype with Hb North Shore previously reported, is confirmed in this study.

Adult↗

PubMed1987

Hemoglobin Hobart or alpha 20(Bl)His----Arg: a new alpha chain hemoglobin variant.

A new alpha chain hemoglobin variant, Hb Hobart, alpha 20(Bl)His----Arg, was detected in a 60-year-old female of British nationality. The proposita had a history of severe rheumatoid arthritis and had been treated for many years for a refractory microcytic anemia and/or iron deficiency. A hemoglobin electrophoresis screen indicated the presence of a hemoglobin variant, with electrophoretic characteristics similar to a Hb Lepore. However, the level of the variant (17.9%) and the presence of a minor variant Hb A2 band (0.4%) suggested that further investigation was indicated. The variant hemoglobin was purified by column chromatography and the alpha chain subjected to aminoethylation and tryptic digestion. Peptide mapping and amino acid analysis indicated that the histidine residue 20 had been substituted by an arginine residue. The substitution in Hb Hobart is at the first residue in the B Helix of the alpha chain of hemoglobin. As this is an externally placed amino acid in the hemoglobin molecule, a substitution at this position of the hemoglobin molecule would not be expected to cause any functional problems. A family study has shown that at least three other relatives are heterozygous for Hb Hobart. These family members have normal hematological findings.

Amino Acids↗

PubMed1984

Haemoglobin D Punjab. Interaction with alpha thalassaemia and diagnosis by gene mapping.

A family which illustrates the inheritance of Hb D Punjab (a beta globin chain variant) and alpha thalassaemia is described. Interaction between Hb D Punjab and alpha thalassaemia is observed since levels of Hb D vary according to the number of alpha globin genes deleted. The technique of gene mapping has been utilised in the current study to provide definitive evidence of alpha thalassaemia and also demonstrates a novel way to identify Hb D Punjab.

Adult↗

PubMed1980

Hemoglobin Westmead alpha 2 122(H5)His replaced by Gln beta 2: a new hemoglobin variant with the substitution in the alpha 1 beta 1 contact area.

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Adult↗

PubMedDate not supplied

On-line interactive evaluation in course and clinical instruction.

Student evaluations incorporated into feedback for instruction modification are an important aspect of any educational program. It is particularly important for healthcare programs in which teaching processes are continually dynamic. An interactive evaluation was designed and implemented on-line for students. Confidentiality was assured and privacy protected through a unique coding system. Our experience with the interactive, automated system proved particularly successful with respondents and faculty expectations have improved since its integration into course and clinical objectives.

Attitude of Health Personnel↗