Key enzymes of the kallikrein-kinin system in antarctic teleosts

In this study, some of the mammalian kallikrein-kinin system (KKS)-like components were identified in two species of Antarctic notothenioid [Chionodraco hamatus (Channichthydae) and 1remato- mus bernacchii (Nothothenidae)]. The kidney and heart were assayed for kallikrein-like activity using the syn- thetic substrate D-Val-Leu-Arg-paranitroanilide. Values expressed as nmol p-nitroanilide/mg proteins, were in C. hamatus 15.5$1.5 and 15.2$1.4 in kidney and heart, respectively, and 15.8$2.2 and 15.9$1 in kid- ney and heart of 1. bernacchii. Kallikrein-like activity was inhibited by aprotinin and phenylmethylsulfonyl fluoride (PMSF). The assay was stable at 20°C. Kininase II-like activity was performed on kidney, gills and heart using the substrate hippuryl-L-histidyl-L- leucine. The activity was inhibited by captopril, and in kidney and gills by high temperatures (20°C and 37°C); in the heart the enzymatic activity was measurable also at 20°C. Bradykinin-like immunoreactive cells were localized by immunohistochemistry in the nephron, in the gills, and in the arterial walls of the heart. These results show that Antarctic teleosts possess elements comparable to those of the KKS, including kallikrein- like, and kininase II-like activities, and the end product of the enzymatic cascade, bradykinin. The enzymatic cascade appears to be fully active only at low temper- atures.