Arginine kinase and phosphoarginine, a functional phosphagen, in the rhabditoid nematode Steinernema carpocapsae

Moderate activity of arginine kinase was found in Steinernema, carpocapsae, an entomopathogenic nematode. In the forward reaction, 4.60 and 3.12 mu mo l ATP/min/mg protein was produced in infectious third-stage juveniles (J3s) and adult nematodes, respectively. For the reverse reaction, 3.20 and 2.27 mu mol phosphoarginine/min/mg protein was produced by J3s and adults, resp ectively. The K(m)s for phosphoarginine and ADP were 0.73 and 0.42 mM, resp ectively, in the forward reaction, whereas in the reverse reaction, the K(m )s were 0.37 and 2.35 mM for arginine and ATP, respectively, for the enzyme from J3s. The pH optimum for the forward reaction was 7.2 and 7.3 in J3s a nd adults, respectively. The pH optimum was elevated for the reverse reacti on, 7.8 and 7.9-8.5 in J3s and adults, respectively. In the J3s, the in vit ro optima for arginine kinase activity was correlated with the in vivo tiss ue pH in hypoxic (6.9) and aerobic (7.5) J3s estimated by in vivo flow P-31 -NMR.