EC 4.1.99 - Photolyase, Deoxyribodipyrimidine Photo-Lyase, Tryptophanase, Tyrosine Phenol-Lyase, Benzylsuccinate Synthase (Paperback)

Chapters: Photolyase, Deoxyribodipyrimidine Photo-Lyase, Tryptophanase, Tyrosine Phenol-Lyase, Benzylsuccinate Synthase, Octadecanal Decarbonylase. Source: Wikipedia. Pages: 20. Not illustrated. Free updates online. Purchase includes a free trial membership in the publisher's book club where you can select from more than a million books without charge. Excerpt: Photolyases (EC 4.1.99.3) are DNA repair enzymes that repair damage caused by exposure to ultraviolet light. This enzyme mechanism requires visible light, preferentially from the violet/blue end of the spectrum, and is known as photoreactivation. Photolyases bind complementary DNA strands and break certain types of pyrimidine dimers that arise when a pair of thymine or cytosine bases on the same strand of DNA become covalently linked. These dimers result in a 'bulge' of the DNA structure, referred to as a lesion. The more common covalent linkage involves the formation of a cyclobutane bridge. Photolyases have a high affinity for these lesions and reversibly bind and convert them back to the original bases. Photolyases are flavoproteins and contain two light-harvesting cofactors. All photolyases contain the two-electron-reduced FADH; they are divided into two main classes based on the second cofactor, which may be either the pterin methenyltetrahydrofolate (MTHF) in folate photolyases or the deazaflavin 8-hydroxy-7,8-didemethyl-5-deazariboflavin (8-HDF) in deazaflavin photolyases. Although only FAD is required for catalytic activity, the second cofactor significantly accelerates reaction rate in low-light conditions. The enzyme acts by electron transfer in which the reduced flavin FADH is activated by light energy and acts as an electron donor to break the pyrimidine dimer. Photolyase is present and functional in many species, from the bacteria to the fungi to the animals. It has not been found in human cells, however, many higher eukaryotes including humans possess a...More: http: //booksllc.net/?id=324993