TAILIEUCHUNG - Báo cáo khoa học: Reaction mechanisms of thiamin diphosphate enzymes: defining states of ionization and tautomerization of the cofactor at individual steps

We summarize the currently available information regarding the state of ionization and tautomerization of the 4¢-aminopyrimidine ring of the thia-mine diphosphate on enzymes requiring this coenzyme. This coenzyme forms a series of covalent intermediates with its substrates as an electro-philic catalyst, and the coenzyme itself also carries out intramolecular pro-ton transfers, which is virtually unprecedented in coenzyme chemistry. | MINIREVIEW Reaction mechanisms of thiamin diphosphate enzymes defining states of ionization and tautomerization of the cofactor at individual steps Natalia S. Nemeria Sumit Chakraborty Anand Balakrishnan and Frank Jordan Department of Chemistry Rutgers The State University of New Jersey Newark NJ USA Keywords 1 4 -iminopyrimidine tautomeric form of thiamin benzaldehyde lyase benzoylformate decarboxylase CD enamine intermediate pyruvate decarboxylase pyruvate dehydrogenase thiamin diphosphate Correspondence N. S. Nemeria 73 Warren Street Newark NJ 07102 USA Fax 1 973 353 1264 Tel 1 973 353 5727 E-mail nemeria@ F. Jordan 73 Warren Street Newark NJ 07102 USA Fax 1 973 353 1264 Tel 1 973 353 5470 E-mail frjordan@ Received 23 October 2008 revised 4 February 2009 accepted 9 February 2009 We summarize the currently available information regarding the state of ionization and tautomerization of the 4 -aminopyrimidine ring of the thiamine diphosphate on enzymes requiring this coenzyme. This coenzyme forms a series of covalent intermediates with its substrates as an electrophilic catalyst and the coenzyme itself also carries out intramolecular proton transfers which is virtually unprecedented in coenzyme chemistry. An understanding of the state of ionization and tautomerization of the 4 -aminopyrimidine ring in each of these intermediates provides important details about proton movements during catalysis. CD spectroscopy both steady-state and time-resolved has proved crucial for obtaining this information because no other experimental method has provided such atomic detail so far. doi Introduction Mindful of the fact that there are several reviews on the enzymology of thiamin diphosphate ThDP the vitamin B1 coenzyme for structures of small molecules mentioned in the present review see Fig. 1 available in the literature 1-15 the present review aims to concentrate on the tautomeric and ionization states of ThDP on enzymes .

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