Purine production during fasting in the slug, Limax flavus linne

Abstract

AbstractThe slug, Limax flavus, reduces hepatopancreatic rates of purine synthesis during fasting. Total body purines decreased during fasting from 661 μg/g wet wt to 384 μg/g wet wt. Slugs fed ad libitum contained 1.5, 2.4 and 2.5 as much uric acid, xanthine and guanine as did slugs fasted for 20 to 23 days. Adenine and hypo‐xanthine were detected inconsistently in the active feeding slugs, where values ranged from 0‐78 μg/g wet wt and 0‐94 μ/g wet wt, respectively (14C glycine‐incorporation). Rates of purine synthesis also decreased with fasting. In active feeding slugs, synthetic rates for adenine, guanine, hypoxanthine, uric acid and xanthine were 17, 36, 14, 138 and 49 nmole/g/d, while in the fasting animals the rates were 2, 9, 0, 81 and 20 nmole/g/d, respectively. The rate of purine production dropped by 56% or a factor of 2.27, which was similar to the decrease in body purines (42% or 1.72 with fasting). Slug hepatopancreatic phosphoribosylpyrophosphate amidotransferase (E.C.2.4.2.14), the enzyme of the first committed step of purine synthesis de novo, was compared with the domesticated chicken liver enzyme. When assayed under the same conditions, both enzymes had similar activities, but differed in that substrate (glutamine) versus velocity plots were sigmoidal for the slug enzyme and hyperbolic for the chicken enzyme. Estimated substrate affinities were Km = 19.0 mM and Km = 2.0 mM for the slug and the chicken enzymes respectively.