E. Brown, M. Konuk
1995
Citations
0
Influential Citations
10
Citations
Journal
Phytochemistry
Abstract
Abstract Biosynthesis of the antibiotic nebularine (purine-9-β- d -ribofuranoside) by Lepista nebularis and Streptomyces yokosukanensis has been studied and a novel enzymic activity is described which deaminates adenosine to release hydroxylamine. Use of 14 C-labelled nucleosides showed that adenosine was the more immediate precursor of nebularine. That formation of nebularine involves direct incorporation of adenosine and does not involve prior catabolism and re-use of catabolic fragments, was shown by locating 82% of the incorporated radioactivity from [8- 14 C]adenosine in C-8 of nebularine. A crude nebularine-forming enzymic extract was fractionated by (NH 4 ) 2 SO 4 precipitation and the activity recovered in the 100% satn supernatant; it was not sedimented by centrifuging for 90 min at 113 000 g. Further purification was achieved by chromatography of Sephacryl S-200 (173-fold) and on BrCN-activated Sepharose 4B (320-fold). Lability of the enzyme during concentration, by various techniques, obviated sequential use of these steps. Activity was not stimulated by pyridine nucleotides or flavins, and a range of metal ions were without effect. Various purine riboside analogues were not inhibitory, although some end-product inhibition was seen with nebularine. Gel-filtration and SDS-PAGE indicated a M r of 9500–10000 for the enzyme. That hydroxylamine is a product of the catalysed reaction was demonstrated chemically and by MS. Use of [ 15 N-amino]adenosine confirmed that the hydroxylamine originates from the 6-amino group of adenosine. The quantitative relationship between nebularine production and metabolism of adenosine to other compounds was studied. Of the total radioactivity from [8- 14 C]adenosine recovered, 3% was in nebularine. The work describes the first reported natural occurrence, in a free state, of purine and its 5′-ribotide.