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Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 343 records · Page 19Linked to original sources
PubMed1977

Hemoglobin Tarrant: alpha126(H9) Asp leads to Asn. A new hemoglobin variant in the alpha1beta1 contact region showing high oxygen affinity and reduced cooperativity.

Hemoglobin (Hb) Tarrant was detected by its electrophoretic mobility on cellulose acetate (pH 8.4) and citrate agar (pH 6.2). On cellulose acetate it moved as a band between hemoglobins F and S, and on citrate agar as a band at hemoglobin S. The test for solubility in 2 M phosphate buffer with Na2S2O4 was negative. The new variant has a substitution of asparagine for aspartic acid in position 126 of the alpha-chain, one of the sites involved in the alpha1beta1 contact. Furthermore, in deoxyhemoglobin aspartic acid 126 of each alpha chain also forms a non-covalent electrostatic salt bridge with arginine 141 of the corresponding alpha chain (Perutz, M. F. and Ten Eyck, L. F. (1972) Cold Spring Harbor Symp. Quant. Biol. 36, 295-310 and Perutz, M. F. (1970) Nature 228, 726-739). As a consequence of this substitution in hemoglobin Tarrant, the deoxy conformation or T state is destabilized because these two bridges cannot be formed. This condition is reflected in high oxygen affinity and low cooperativity.

Amino Acid Sequence↗
PubMed1977

Changes in protein synthesis during maturation of sheep oocytes in vivo and in vitro.

The qualitative profiles of the proteins synthesized by sheep oocytes at various stages of maturation were determined by electrophoretic separation in one dimension on polyacrylamide SDS gels. No change in protein synthetic pattern was observed in ooce changes had taken place in at least 12 separate protein bands. Marked alterations in the synthesis of some proteins were apparent 15 h after LH; formation of proteins in 5 of the original bands was either reduced or not detectable, while new synthesis was evident from the appearance of 7 additional bands. The pattern of proteins produced by oocytes cultured within the follicle corresponded closely with that observed in vivo: changes in synthesis were initiated about 9 h after addition of gonadotrophin and were completed by 15 h. Oocytes cultured outside the follicle in a gonadotrophin-containing medium did not exhibit a change in protein synthesis and at 15 h only those proteins produced during the early stages of maturation were being synthesized.

Animals↗
PubMed1977

The progesterone content of rabbit uterine flushings.

A detailed study has been made of the progesterone content of uterine flushings taken from rabbits of different endocrine states. A high content of progesterone was recovered from the uterine lumen of pregnant and pseudopregnant rabbits. The amount of progesterone recovered in the flushings was not simply dependent on the concentration in the plasma, because plasma progesterone concentrations rose before detection of progesterone in the flushings and remained high after uterine progesterone content had fallen. Progesterone did not appear in the uterine fluid unless uterine protein was present. This was particularly evident in rabbits treated with progesterone in which, despite abnormally high plasma concentrations, little progesterone was found in uterine fluid until the protein content increased. After treatment of rabbits with oestrogen at the time of ovulation, uterine progesterone was present in higher amounts concomitant with an elevation of protein content although the peak values of progesterone and protein were delayed by 2--3 days. Plasma progesterone concentrations of about 5 ng/ml were necessary before progesterone appeared in the uterine lumen.

Animals↗
PubMed1977

Hemoglobin Lufkin: beta 29 (B11) Gly replaced by Asp. An unstable hemoglobin variant involving an internal amino acid residue.

Hemoglobin Lufkin was found in a Black-American family. Structural analysis of the abnormal hemoglobin indicates a substitution of aspartic acid for glycine at position 29 in the beta chain. Marked instability of the variant hemoglobin is demonstrated by the rapid formation of inclusion bodies upon exposure of the red cells to redox dyes and by the large percentage of precipitated hemoglobin at 65 degrees C. The oxygen affinity, the Bohr effect, and the degree of cooperativity of Hb Lufkin and Hb A are similar over the physiologic pH range. However, at acid pH the oxygen affinity of the variant is increased. Unlike several other reported variants in the B helix, Hb Lufkin is not associated with methemoglobinemia.

Amino Acids↗
PubMed1976

Hemoglobin Fannin-Lubbock [alpha2 beta 2 119 (GH2) Gly replaced by Asp]. A new hemoglobin variant at the alpha1 beta 1 contact.

Hemoglobin Fannin-Lubbock was found in a 9-year-old Mexican-American female. The abnormal hemoglobin was detected as a fast-moving variant by electrophoresis on cellulose acetate at pH 8.4. Structural analysis indicated a substitution in the beta-chain of aspartic acid for glycine at position 119, a position involved in the alpha1beta1 contact of the hemoglobin tetramer. This contact between unlike chains is larger and undergoes a smaller shift during the process of oxygenation and deoxygenation that the alpha1beta2 contact (Perutz, M.F., Muirhead, H., Cox, J.M. and Goaman, L.C.G. (1968) Nature 219, 131-139). Mutations in this contact tend to cause slight or no changes in functional behavior. Apart from a mild anemia, the propositus did not exhibit any obvious clinical symptoms.

Amino Acids↗
PubMed1976

Hemoglobin Providence. A human hemoglobin variant occurring in two forms in vivo.

Hemoglobin Providence Asn and Hemoglobin Providence Asp are two abnormal hemoglobins which apparently arise from a single genetic change that substitutes asparagine for lysine at position 82 (EF6) in the beta chain of human hemoglobin. The second form appears to be thr result of a partial in vivo deamidation of the asparagine situated at position beta 82. Cellulose acetate and citrate agar electrophoresis of hemolysates from patients with this abnormality shows three bands. Globin chain electrophoresis at acid and alkaline pH shows three beta chains. These three chains correspond to the normal beta A chain and two abnormal beta chains. Sequence analysis indicates that the two abnormal chains differ from beta A at only position beta 82. In the two abnormal chains, the residue which is normally lysine is substituted either by asparagine or by aspartic acid. These substitutions are notable because beta 82 lysine is one of the residues involved in 2,3-diphosphoglycerate binding. Additionally, beta 82 lysine is typically invariant in hemoglobin beta chain sequences. Sequence data on the two forms of Hemoglobin Providence are given in this paper. The functional properties of these two forms are described in the next paper.

Adult↗
PubMed1976

Hemoglobin Jackson, alpha 127 (H10) Lys replaced by Asn.

A new hemoglobin mutant was detected as a fast-moving variant on cellulose acetate electrophoresis at pH 8.4. The mutation is in the alpha-chain at position 127, where lysine is substituted by asparagine. This is an external residue, and mutation at this site does not lead to any altered physiologic function of the hemoglobin.

Adult↗
PubMed1976

Ultrastructural studies on the surface membrane of the mouse egg.

Fertilized and unfertilized mouse eggs were examined by scanning and transmission electron microscopy for evidence of mosaicism in the organization and concanavalin A-binding properties of their surface membranes. No obvious quantitative mosaicism in concanavalin A binding was noted. The egg membrane was microvillous over most of its surface, but was smooth in the region overlying the 2nd metaphase spindle of the unfertilized egg and on the polar body of the fertilized egg.

Animals↗
PubMed1976

The nature and distribution of serologically detectable alloantigens on the preimplantation mouse embryo.

The nature and distribution of surface alloantigens on preimplantation mouse embryos has been examined by immunofluorescence. Non-H-2 alloantigens were detected at all stages examined, from the 2-cell to the 4 1/2-day blastocyst. Cleaving blastomeres, inner cell mass cells and cells of the primary trophectoderm were all positive. In F1 embryos maternal non-H-2 alloantigens were detectable at all stages, whereas paternal antigens first became evident at the 6- to 8-cell stage. No convincing evidence of the presence of alloantigens associated with the H-2 haplotype was found at any stage or on any cell type, suggesting that if these antigens are present they are in low quantity or are masked.

Animals↗
PubMed1975

Investigation of cellular interaction and deployment in the early mammalian embryo using interspecific chimaeras between the rat and mouse.

Mammalian chimaeras can be produced experimentally by aggregating early embryos or by injecting cells into them. They have been used to study several aspects of early development. However, lack of a genetic marker enabling unequivocal identification of all cells of either genotype in situ has frustrated full exploitation of the experimental possibilities offered by these organisms. Hence interspecific chimaeras have been produced between rat and mouse embryos in which cells of the two species can be identified in sectioned embryos by immune fluorescence. These chimaeric embryos have been used to study differentiation of the trophoblast and inner cell mass, and the deployment of cells during morphogenesis. Preliminary results suggest that the two tissues are determined by the blastocyst stage, and that the trophoblast forms part of the extra-embryonic membranes originally presumed to be derived from the inner cell mass. Also, rat inner cell mass cells can induce mitosis in mouse trophoblast. Futhermore, the distribution of rat cells in implanted embryos suggests that the embryo may grow in a coherent clonal manner from a very early stage. Very recently, chimaerism has been induced by transplanting single rat cells, which may allow a more critical analysis of morphogenesis and determination than was possible hitherto. An obvious question raised by crossing the species barrier is the extent to which results may be applicable to normal development. Adverse effects of immunological interaction between the mouse uterine foster-mother and fetal rat cells, and sorting out of cells according to species, are two of the problems that might complicate interpretation of these experiments.

Animals↗
PubMed1975

Interrelationships among patients, medical students and resident psychiatrists.

The authors have investigated the interrelationships among psychiatric resident physicians, medical student clerks, and patients on the inpatient psychiatric wards in two teaching hospitals. Medical students tended to focus on establishing rapport with patients whereas psychiatric residents tended to focus on psychopathology and management.

Attitude of Health Personnel↗