Effects of hypoxia and toxicant exposure on arginine kinase function as measured by 31P-NMR magnetization transfer in living abalone
The activity of arginine kinase (AK) was evaluated by saturation transfer NMR in red abalone (Haliotis rufescens) in response to hypoxia, sodium azide (NaN3; an inhibitor of cytochrome c oxidase), or penta chlorophenol (PCP; an uncoupler of oxidative phosphorylation) exposure Pseudo-first order rate constants (K(for)) in the forward (ATP forming) reaction direction showed maximal increases from basal values of 0.025 s-1 0.095, 0.114, 0.126 s-1 for NaN3 hypoxia, and PCP exposures, respectively. Increases in K(for) were inversely correlated (r2 = 1.00) to declines in ATP concentration in all exposed animals. Flux (the product of K(for) and phosphsarginine concentration) appeared to converge on a common value, from basal flux values of 0.257 mM PA, s-1 to 0.703, 0.770, and 0.627 mM PA s-1 for NaNs, hypoxia, and PCP exposures, respectively. It seems likely that all three stresses were equally effective at inhibiting mitochondrial ATP formation, which may account for the similarity in flux increase, possibly to maximal rates of AK-mediated ATP formation. Differences in K(for) are related to declines in ATP concentrations, which appear to be stress specific, and likely indicate additional mechanisms of toxicity for NaN3 and PCP.
