Alteration of 5′-nucleotidase Properties in Rat Adipose and Liver Plasma Membranes after 1 Gy Whole-body γ-irradiation

Abstract

5′-Nucleotidase activites in rat adipose and liver plasma membranes (PM) were examined at various times after 1 Gy whole-body γ-irradiation. Changes in the enzyme kinetic parameters were recorded 6 and 14 weeks after exposure: K_m decreased while V_max increased. The enzyme in control PM showed temperature-dependent Arrhenius plots with a lower activation energy at temperatures above a break point at ∼28°C, whereas 5′-nucleotidase in irradiated PM showed a constant activation energy between 10 and 40°C which was reasonably close to the value observed controls at temperatures below the break point. Furthermore, the interaction of [³H]-AMP with the 5′-nucleotidase catalytic site was studied on adipose PM using a rapid filtration technique. γ-Irradiation was associated with an increased number of specific AMP-binding sites and decreased ligand affinity. Comparison of the presented data with previous work (Yegutkin et al. 1993a,b) indicate significant functional and structural modification of rat adipose and liver PM following 1 Gy γ-irradiation and reveals interrelation of these changes.