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KMID : 0376219660030010041
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Chonnam Medical Journal
1966 Volume.3 No. 1 p.41 ~ p.51
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Hydrolysis` of Nicotinamide Mononucleotide by NAD Glycohydrolase and Enzymic Synthesis of 5-Amino-4-imidazolecarboxamide Ribotide by Transglucosidation
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Abstract
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1. Nicotinamide adenine dinucleotide glycohydrolase (NADase) has been partially purified from rabbit brain acetone powder and shown to catalyze the hydrolysis of .nicotinamide mononucleotide (NMN) at the nicotinamide riboside bond. Evidence is presented indicating that it also functions as transglucosidase for NMN by demonstrating the direct formation of 5-amino-4-imidazolecarbox- amide (AICA) ribotide from AICA and NMN.
2. The hydrolysis of NAD by NADase was competitively inhibited by NMN and the concentration of NMN for the 50% inhibition was found to be 1.3x10-3 M.
The activities of NADase for NAD and for NMN could not be separated from each other and there was little change in the ratio of both activities (NADase/NMNase) during purification. The Michaelis constant (Km) for NMN Was found to be the same as for NAD (Km=8x10-4M).
3. The hdrolysis of NMN by NADase was also inhibited by nicotinamide and the exchange of free nicotinamide with the bound nicotinamide in NMN was demonstrated using nicotinamide-7-14C.
4. In addition the enzyme also catalyzes the direct formation of-AICA ribotide by transferring ribose-5-phosphate group from NMN to AICA. The reaction was found to be proportional to the incubating time and to the concentration of the enzyme and also inhibited by nicotinamide added in vitro.
5. AICA-14C ribotide was prepared on a large scale by reacting NMN and AICA-14C in the presence of brain NADase and was identified.
6. From these results, the possibility is suggested to indicate that NMN might function in nucleotide biosynthesis as a donor of ribose-5-phosphate group to nitrogenous bases by the action of NADase.
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KEYWORD
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