Digestive enzymes of the salmon louse (Lepeophtheirus salmonis) : implications for vaccine development
This study identified potential salmon louse gut antigens and determines the fate of salmon antibodies in the louse gut. The characteristics and distributions of three salmon louse (Lepeophtheirus salmonis) gut enzymes, aminopeptidase (SLAP), alkaline phosphatase (LAlkP) and β-acetyl-hexosaminidase (LHex) are described. SLAP preferred terminal methionine residue substrates and was inhibited by leuhistin, amastatin and bestatin, identifying it as an aminopeptidase N-type enzyme. Chelators inhibited SLAP activity, and Zn2+ reactivated SLAP after chelation. The enzyme was inhibited by Zn2+, Cu2+ and at 50 mM Ca2+, and activated by Mn2+ and Mg2+, SLAP activity was highest at pH 7.5 – 8.5. SLAP is a novel aminopeptidase as its activity was increased by molar concentrations of both NaC1 and KC1. The enzyme is present in soluble and membrane-associated enzyme forms. LAlkP activity was highest at pH 9 – 9.5 and required bound metal cations for catalysis with both Zn2+ and Mg2+ being able to re-activate the enzyme after chelation. LAlkP activity was also increased by molar concentrations of NaC1 and MK1. LAlkP was predominantly present as a membrane-associated enzyme. LHex activity was greatest at pH 6.5 – 7, and inhibited by N-acetyl-galactosamine and N-acetyl-glucosamine. LHex was partially inhibited by molar concentrations of NaC1, but was relatively tolerant to high salt concentrations. LHex was unaffected by chelation by EDTA. LHex was most able to resist denaturation by urea. SLAP was stabilised and activated by NaC1 and TMAO. LAlkP activity was increased by NaC1 but not by TMAO, due likely to factors not associated with stability, such as ionic forces increasing the rate of dephosphorylation. LHex was inhibited by the kosmotropic effects of both TMAO and NaC1.