Preservation of phosphagen kinase function during transient hypoxia via enzyme abundance or resistance to oxidative inactivation

Abstract

Mammalian lactate dehydrogenase and phosphofructokinase are more susceptible in vitro to superoxide$(O_2^{\dot - } )$ and hydroxyl (·OH) radicals than pyruvate kinase and glucose-6-phosphate dehydrogenase, suggesting that differential inactivation of regulatory enzymes contributes to the metabolic disintegration in stenoxic tissues during transient hypoxia. Like-wise, creatine kinase in smooth muscle from porcine ileum is significantly reduced by hypoxia-reoxygenation ex vivo from 300 (±18.2 SE,n=8) to 196 U·g wet wt^-1 (±16.7,P0.001, ANOVA). Conversely, arginine kinase, from the myocardium ofLimulus polyphemus, a species that tolerates anoxia for days was 2.9-fold less susceptible to oxidative inactivation. To examine whether preservation of kinase function is related to euryoxic capacity, a combination of non-invasive³¹P-NMR spectroscopy and enzyme-linked assays was used to follow ATP and phosphagen status during hypoxia-reoxygenation in porcine ileum smooth muscle,L. polyphemus myocardium, and the myocardium ofArgopecten irradians, a scallop species tolerant of hypoxia for only 24 h. Despite wide differences in phylogeny, euryoxic capacity and oxidative vulnerability of the phosphagen kinases, in all three tissues, the phosphagen pool recovered concomitant with ATP during reoxygenation, thereby revealing competent kinase function. In the mammalian tissue, such preservation of kinase function is facilitated by a 2400-fold excess of enzyme activity.