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 pLmol 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 pxmol phosphoarginine/min/mg protein was produced by J3s and adults, respectively. The Kms for phosphoarginine and ADP were 0.73 and 0.42 mM, respectively, in the forward reaction, whereas in the reverse reaction, the Kms 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 and adults, respectively. The pH optimum was elevated for the reverse reaction, 7.8 and 7.9-8.5 in J3s and adults, respectively. In the J3s, the in vitro optima for arginine kinase activity was correlated with the in vivo tissue pH in hypoxic (6.9) and aerobic (7.5) J3s estimated by in vivo flow 31P-NMR. Thompson et al. (1990) observed a phosphagen, phosphoar- ginine, in infectious third-stage juveniles (J3s) of Steinerema carpocapsae (an entomopathogenic nematode) by employing in vivo flow 31P-NMR spectroscopy. In this procedure, suspen- sions of juvenile nematodes were circulated continuously through the spectrometer. Phosphoarginine was the major peak in the phosphorous spectrum of S. carpocapsae maintained un- der aerobic conditions, but its level declined rapidly during hyp- oxic conditions. As oxygen tension decreased, changes in the relative levels of phosphoarginine and ATP were consistent