PURIFICATION OF L-ARGININE KINASE FROM THE TOBACCO BUDWORM, HELIOTHIS-VIRESCENS [NOCTUIDAE] AND ITS FUNCTION IN L-CANAVANINE DETOXIFICATION

Larval tobacco budworm, Heliothis virescens [Noctuidae] are aggressive , generalist feeders that tolerate high levels of dietary L-canavanine , an insecticidal L-arginine antimetabolite; the LC(50) for dietary ca navanine is 300 mM, Arginine kinase (adenosine 5' triphosphate: L-argi nine phosphotransferase, EC 3.5.3.1), which mediates a phosphorylation of canavanine to yield the novel phosphagen, L-canavanine phosphate, was purified from larval gut, Kinetic parameters revealed an apparent K-m value of 7.2 x 10(-4) and 2.13 x 10(-2) M for arginine and canavan ine, respectively, These K-m values suggest that arginine kinase's aff inity for canavanine is substantially less than its affinity for argin ine, The ability of arginine kinase to metabolize canavanine accounts for the enhancement in canavanine catabolism in the presence of ATP ob served in canavanine-treated larvae, Canavanine is a more effective su bstrate for arginine kinase than homoarginine, 2-amino-4-guanidinobuty ric acid, and 2-amino-3-guanidinopropionic acid. However, all the argi nine analogs were more active suhstrates for arginine kinase than homo canavanine and 2-amino-3-guanidinooxypropionic acid, the higher and lo wer canavanine analogs, respectively, When arginine kinase reacted wit h N-tris[hydroxymethyl]methylglycine (tricine) massive amounts of an u nidentified, but ninhydrin-positive product was formed. The larvae sho wed no detectable loss in their ability to deal with dietary canavanin e in the presence of tricine buffer.