Abstract
Haemophilus haemoglobinophilus, a species of Haemophilus which is not dependent upon NAD for growth, was investigated with regard to the pathway of biosynthesis synthesis of this cofactor. Cell-free extracts synthesized NAD directly from nicotinamide without prior deamidation via the following reactions: Nicotinamide+5-phosphoribosyl 1-prrophosphate+ATP → NMN NMN+ATP → NAD Of the enzymes known to be operative in the pathway of NAD biosynthesis from nicotinic acid (nicotinate phosphoribosyltransferase, nicotinate adeninedinucleotide pyrophosphorylase and NAD synthetase) only nicotinate phosphoribosyltransferase activity was demonstrable. Cell free extracts of H. haemoglobinophilus did not degrade NAD and nicotinamidase activity was absent. Quinolic acid was not converted to NAD. The results obtained provided evidence that this organism cannot recycle NAD or synthetize it via the de novo pathway. Direct synthesis from nicotinamide via NMN appears to be the sole pathway of NAD formation in this organism.
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