Some kinetic studies on ribonucleosides degradation by extracts of penicillium citrinum

✍ Scribed by A. M. Allam; T. A. Elzainy; M. A. Elsayed; A. M. Elshafei

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 355 KB
• Volume: 11
• Category: Article
• ISSN: 0138-4988
• DOI: 10.1002/abio.370110310

✦ Synopsis

Cell-free extracts 01 3-4 days old mats of nitrate-grown Penicillium citrinum catalyze the hydrolytic cleavage of the N-glycosidic bonds of inosine, guanosine and adenosine optimally a t pH 4, 0.1 hl citrate buffer. The same extracts catalyze the hydrolytic deamination of cytidine a t a maximum rate in 0.08 M Tris-acetate buffer pH 6.5, 40' and 50°C were the most suitable degrees for purine nucleoside hydrolysis and cytidine deamination, respectively. The incubation of the extract.s a t 60°C. in the absence of cytidine caused a loss in the deaminating activity, while freezing and thawing had no effect on both activities. The deaminating activity seems to be cytidine specific as neither cytosine, adenine, adenosine nor guanosine could be deaminated. Uridine competively inhibited this activity, while ammonia had no effect. The apparent K,,, value of this enzyme for cyt,idine was 1.57 x i C r 3 M and its Ki value for uridine was 7.8 x 10-3 31. The apparent K,,, values of the N-glycosidic bond cleaving enzyme for inosine, gnanosine and adenosine were 13.3, 14.2 and 20 )c 10-% 31, respectively.