| photo-patch test | A test of contact photosensitization: after application of a patch with the suspected sensitiser for 48 hours to two sites, if there is no reaction one area is exposed to a weak erythema dose of sunlight or ultraviolet light; if positive, a more severe reaction with vesiculation develops at the exposed patch area than the nonexposed skin patch site. (05 Mar 2000) |
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| photoablation | <technique> The destruction of cells by the action of light (16 Dec 1997) |
| photoactinic | Denoting radiation that produces both luminous and chemical effects. Origin: photo-+ G. Aktis, ray (05 Mar 2000) |
| photoaffinity labelling | <technique> A technique for covalently attaching a label or marker molecule onto another molecule such as a protein. The label, which is often fluorescent or radioactive, contains a group that becomes chemically reactive when illuminated usually with ultraviolet light) and will form a covalent linkage with an appropriate group on the molecule to be labelled: proximity is essential. The most important class of photoreactive groups used are the aryl azides, which form short lived but highly reactive nitrenes when illuminated. (31 Dec 1997) |
| photoaffinity labels | Biologically active molecules which are covalently bound to the enzymes or binding proteins normally acting on them. Binding occurs due to activation of the label by ultraviolet light. These labels are used primarily to identify binding sites on proteins. (12 Dec 1998) |
| photoallergic sensitivity | See: photosensitization. (05 Mar 2000) |
| photoallergy | See: photosensitization. (05 Mar 2000) |
| photoautotroph | <biology> An organism able to use light as its sole source of energy and carbon dioxide as sole carbon source. (09 Oct 1997) |
| photoautotrophic | Pertaining to a photoautotroph. (05 Mar 2000) |
| photobacteria | Plural of photobacterium. (05 Mar 2000) |
| photobacterium | A genus of gram-negative, facultatively anaerobic, rod-shaped bacteria that are common in the marine environment and on the surfaces and in the intestinal contents of marine animals. Some species are bioluminescent and are found as symbionts in specialised luminous organs of fish. (12 Dec 1998) |
| Photobacterium harveyi | lucibacterium harveyi |
| Photobacterium phosphoreum | A luminescent species found on dead fish and in sea water; it is the type species of the genus Photobacterium. (05 Mar 2000) |
| photobiology | The branch of biology which deals with the effect of light on living organisms. (12 Dec 1998) |
| photobiotic | <biology> Requiring light to live; incapable of living without light; as, photobiotic plant cells. Origin: Photo- + biotic. Source: Websters Dictionary (01 Mar 1998) |