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M Morrison

Publications and source records attributed to M Morrison.

12 recordsLinked to original sources
PubMed1979

Effect of endo-beta-galactosidase on intact human erythrocytes.

Endo-beta-galactosidase, a glycosidase that hydrolyzes Gal beta 1-4 GlcNAc linkages in glycoconjugates, has been used to probe the plasma membrane of human erythrocytes. Coomassie blue staining of stroma components separated by sodium dodecyl sulfate-acrylamide gel electrophoresis indicates that treatment of red cells with endo-beta-galactosidase converts Protein 3, the anion transporter of the erythrocyte, to a more compact staining band. No other components detected by Coomassie staining are affected. Following labeling of red cells with galactose oxidase + NaB3H4, 45 to 50% of the [3H]galactose residues can be released by endo-beta-galactosidase. In contrast, only 5% of the label incorporated by treatment with periodate + NaB3H4, can be removed. [3H]Galactose residues are released from three components: Protein 3, Band 4.5, and the megaloglycolipids. The susceptibility of these components to endo-beta-galactosidase, together with the high content of Gal and GlcNAc present in Protein 3 and the megaloglycolipids, suggests that the erythrocyte membrane contains several components with N-acetyllactosamine repeating units, a structure commonly found in connective tissue glycoconjugates.

Erythrocyte Membrane↗
PubMed1979

Distribution of transmembrane polypeptides in freeze fracture.

Human erythrocytes have been freeze-fractured, and the polypeptides associated with the separate halves of the membrane bilayer have been analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The transmembrane proteins were differentially separated by the fracture process. Although sialoglycoproteins associated with the outer half of the membrane, the anion transport protein (band 3) mainly remained with the inner half of the membrane. Well-defined fragments of the sialoglycoproteins were produced by the freeze-fracture procedure, indicating that selected covalent bonds of these transmembrane proteins were broken.

Erythrocyte Membrane↗
PubMed1977

Lactoperoxidase-catalyzed iodination of horse cytochrome c:monoiodotyrosyl 74 cytochrome c.

Iodination of horse cytochrome c with the lactoperoxidase-hydrogen peroxide-iodide system results initially in the formation of the monoiodotyrosyl 74 derivative. This singly modified protein was obtained in pure form by ion exchange chromatography and preparative column electrophoresis. It shows an intact 695 nm absorption band, the midpoint potential of the native protein, a nuclear magnetic resonance spectrum which indicates an undisturbed heme crevice structure, a normal reaction with antibodies directed against native horse cytochrome c, and circular dichroic spectra in which the only changes from those of the native protein can be ascribed to the spectral properties of iodotyrosine itself. This conformationally intact derivative reacts with the succinate-cytochrome c reductase and the cytochrome c oxidase systems of beef mitochondrial particle preparations indistinguishably from the unmodified protein, showing that the region including tyrosine 74 is not involved in these enzymic electron transfer functions of the protein. The circular dichroic spectra of this derivative indicate that the minima observed at 288 and 282 nm in the spectrum of native ferricytochrome c originate from tyrosyl residue 74.

Animals↗
PubMed1976

Peroxidase-catalyzed halogenation.

Peroxidase-catalyzed halogenation reactions have been established as being important in the biosynthesis of the hormone thyroxine and in biological defense mechanisms. Recently these reactions have been recognized as valuable tools for the study of proteins as well as their arrangement in macromolecular structures. The pathways of peroxidase catalyses can be accommodated within the framework of the classical Chance-George mechanism. This implies that the initial steps of the reaction invariably involve oxidation of peroxidases by peroxides--and that the resulting derivative, compound I, is the oxidant of the halide ions. Such reactions may result either in the formation of hypohalous acids, or in halogenation of the enzyme apoprotein, followed by transhalogenation to substrate for halogenation. Chloro- and myeloperoxidases catalyze oxidation of all halide ions, except F-; oxidation of bromide and iodide is mediated by lactoperoxidase, but horseradish peroxidase only oxidizes iodide. All of the above enzymes except horseradish will oxidize the pseudo halide thiocyanate. The origins of this differentiation remain to be defined, but they presumably reflect significant variation in oxidation potential of different peroxidase-peroxide derivatives, rather than constraints on the peroxidase-donor interactions. As pointed out above, halogenation of the amino acids tyrosine and histidine or these residues in proteins can take place on the enzyme. This makes lactoperoxidase-catalyzed iodination selective. The amino acid residues in proteins that are iodinated depend not only on reactivity of the amino acid residue but also on its geometric location. Thus lactoperoxidase-catalyzed iodination can be a useful tool in the study of protein structure and function. It is also useful in establishing the geometric position of proteins within macromolecular structures. Thyroid peroxidase catalyzes iodination of thyroglobulin and is involved in a second important step, the coupling of the iodotyrosines to form thyroxine or triiodothyronine. A proposed mechanism for this reaction suggests that the oxidation is mediated by the iodoenzyme derivative mentioned above followed by a prototropic rearrangement and scission to form the ether bound of thyronine and a serine residue on thyroglobulin.

Amino Acids↗
PubMed1975

Immunological and biophysical properties of hepatitis B antigen labeled by the chloramine-T and by the lactoperoxidase methods.

Optimal conditions were sought for the radiolabeling of microgram quantities of hepatitis B surface antigen (HBs Ag) employing the chloramine-T or lactoperoxidase iodination procedures. Preparations of HBsAg labeled by these procedures are referred to as chloramine-T preparations and lactoperoxidase preparations, respectively. Labeled HBsAg having specific activities between 10-20 muCi/mug were found to display the greatest degree of sensitivity for unlabeled HBsAg and for anti-HBs using a double-antibody radioimmunoassay (RIA-DA). Increasing the specific activity above this level redulted in a decreased affinity of labeled 1251-HBs Ag for anti-HBs, indicating that soluble antigenic alterations had developed. At equivalent specific activities, chloramine-T preparations competed less effectively for unlabeled HBs Ag than lactoperoxidase preparations, and anti-HBs endpoint titers were slightly reduced, especially among preparations of high specific activity (greater than or equal to 65 muCi/mug). Chloramine-T preparations of HBs Ag (sp. act. 15--30 muCi/mug) showed essentially no antigenic deterioration over a 2-month period at minus 196 degrees C or minus 70 degrees C. Utilization of optimally labeled 1251-HBs Ag has increased the sensitivity of the RIA-DA for unlabeled HBs Ag 30-fold to a level below 1 ng/ml and enhanced antiamine-T method revealed that only the most acidic population was labeled (pH 3.75+/-0.5). In contrast, six antigenic components with distinct pI values ranging from 3.7 to 5.2 were detected by RIA-DA in both unlabeled HBs ag and in the chloramine-T preparation. This indicated that the chloramine-T method did not radically change the relative number or charge of each of the pI populations present in purified preparations of HBs Ag. Analysis of HBs Ag iodinated by the lactoperoxidase procedure revealed the presence of three of four populations of particles with pI values ranging from 3.9 to 4.5, suggesting that this procedure labels HBs Ag more uniformly.

Chloramines↗