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PubMed1956

Modification of the homotypic specificity of poliomyelitis complement-fixing antigens by heat.

Fluid obtained from HeLa cell cultures infected with poliomyelitis viruses served as a complement-fixing antigen. When used in the native state, i.e. untreated in any way, the fluids acted as homotypically specific antigens. When heated, however, the antigenicity was broadened and a high degree of heterotypic reactivity was encountered. Data are presented indicating that the observed group reactivity was apparently based on common antigens shared by the three immunologic types of poliomyelitis virus. This reactivity appeared to be specific for the poliomyelitis viruses. No evidence was obtained in preliminary experiments that heating of the antigens releases a "soluble" antigen responsible for the group reactivity.

Antibodies↗

PubMed1958

The thermal stability of rhodopsin and opsin.

Rhodopsin, the red photosensitive pigment of rod vision, is composed of a specific cis isomer of retinene, neo-b (11-cis), joined as chromophore to a colorless protein, opsin. We have investigated the thermal denaturation of cattle rhodopsin and opsin in aqueous digitonin solution, and in isolated rod outer limbs. Both rhodopsin and opsin are more stable in rods than in solution. In solution as well as in rods, moreover, rhodopsin is considerably more stable than opsin. The chromophore therefore protects opsin against denaturation. This is true whether rhodopsin is extracted from dark-adapted retinas, or synthesized in vitro from neo-b retinene and opsin. Excess neo-b retinene does not protect rhodopsin against denaturation. The protection involves the specific relationship between the chromophore and opsin. Similar, though somewhat less, protection is afforded opsin by the stereoisomeric iso-a (9-cis) chromophore in isorhodopsin. The Arrhenius activation energies (E(a)) and entropies of activation (DeltaSdouble dagger) are much greater for thermal denaturation of rhodopsin and isorhodopsin than of opsin. Furthermore, these values differ considerably for rhodopsins from different species -frog, squid, cattle-presumably due to species differences in the opsins. Heat or light bleaches rhodopsin by different mechanisms, yielding different products. Light stereoisomerizes the retinene chromophore; heat denatures the opsin. Photochemical bleaching therefore yields all-trans retinene and native opsin; thermal bleaching, neo-b retinene and denatured opsin.

Animals↗

PubMed1959