English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The problem of biological membrane structure has recently received new impetus from optical rotatory dispersion (ORD) and circular dichroism (CD) studies. Cotton effects arising from electronic transitions of the peptide bond in the ultraviolet have been reported for the plasma membranes of Ehrlich ascites carcinoma cells,' human erythrocytes and Bacillus subtilis membranes,2 submitochondrial vesicles of heavy beef heart mitochondria,3 and chloroplast fragments.4 In addition, the ORD spectra of beef spinal cord myelin, rat liver submitochondrial vesicles, and the membranes of Halobacterium cutirubrum and Micrococcus lysodeikticus have been examined.5 The ORD spectra for all of these materials are remarkably similar, but as a group show unique properties which distinguish them from those of other proteins or synthetic polypeptides. They exhibit the form generally characteristic of an a-helix but differ in several important respects. The most striking deviation is a shift of the entire Cotton effect toward longer wavelengths; i.e., the troughs appear at 235-237 mA rather than the usual 233 mMA, the peaks are at 200-204 m/1 instead of 198-199 m,4, and the crossovers also occur at comparably higher wavelengths. These experiments were carried out at physiological pH. Detergents such as sodium dodecyl sulfate or lysolecithin cause the red shift to vanish, and the ORD curves assume the wavelength parameters characteristic of the usual a-helix. A secondary feature is that although in some cases the shape of the Cotton effect is that of a fully helical polypeptide, the rotational amplitude is too low and cannot be accounted for by the usual combinations of a-helix and random coil. In view of their appearance in a wide variety of membrane systems, these redshifted curves must represent some common structural feature shared by all. Several interpretations have been offered. Wallach and Zahler' suggested hydrophobic interaction of helical protein segments with lipid fatty acid hydrocarbons, Lenard and Singer2 proposed interaction of adjacent protein helices, and Urry, Mednieks, and Bejnarowicz3 interpreted the curves as the sum of lipid and protein rotations. In this communication we will show that the red shift can be explained in terms of the protein portion of the membrane rather than by the lipid or the combination of lipid with protein. We have found that in the absence of lipid the aggregation of structural protein from mitochondria results in a red shift as well as the decreased rotational amplitude characteristic of membranes. Furthermore, this red-shifted ORD spectrum can be reversibly converted to that typical of an a-helix. Experimental.-Materials: The isolation of heavy beef heart mitochondria,6 and the preparation of submitochondrial vesicles7 from them was as previously described elsewhere. Mitochondrial structural protein (MSP) was prepared from heavy beef heart mitochondria according to Richardson, Hultin, and Fleischer.8 The phosphorus content was 0.3 ,ug P/mg protein for the MSP and 18.4 Mg P/mg protein for

Aggregation-induced red shift of the Cotton effect of mitochondrial structural protein.