Consideration of the rate of product

Consideration of the rate of product formation at different substrate concentrations and estimation of Michaelis-Menten parameters gives some insight into the possible mechanisms underlying the observed decreases in enzyme activity. Estimates based on two-substrate concentrations lack precision and statistical analysis of the results did not identify any significant differences between the patient groups, the results do, however, still provide some useful information. Our results indicate that activity of ApB is decreased in early AD and that the decreased activity persists as the disease progresses. Activities of ApA and ApN, on the other hand are significantly decreased only later in the disease. In the case of ApB, the Michaelis-Menten analysis suggests that there is an increase in KM with little or no change in Vmax. An increase in KM suggests that the observed decrease in enzyme activity is a result of decreased affinity of the enzyme for its substrate (conformational change), rather than a change in the concentration of enzyme present (enzyme expression). In the case of ApN, the Michaelis-Menten analysis suggests no change in KM but a decrease in Vmax later in the disease. Such a change would indicate decreased enzyme Cucurbitacin I synthesis with no change in conformation. It was not possible to obtain any reliable estimates of KM or Vmax for ApA, the mechanism underlying the decreased activity in later AD therefore remains unresolved
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Acknowledgements
Introduction The genus Taenia is one of the most prevalent pathogens, which constantly cause severe parasitic diseases in their hosts. Several important tapeworms, such as T. pisiformis, T. ovis, T. multiceps, and T. hydatigena, are mainly transmitted between canines and herbivorous livestock and result in considerable harm to the livestock breeding industry. These adult tapeworms parasitize the intestinal tract of the definitive hosts (canines) and the larval tapeworms invade the brain, liver or omentum of the intermediate hosts (sheep, cattle or rabbit). Tapeworm infections seriously threaten animal health and affect husbandry production (Murrell, 2005). Dogs are a key source of long-term cyclic infection of tapeworms because of the production of infectious eggs. As such, the most cost-beneficial way to control tapeworm infection would be to break directly the transmission of eggs (Chabalgoity et al., 1997). At present, it remains a substantial veterinary challenge to effectively survey, prevent and control tapeworm infections in China because of limitations of vaccine ineffectiveness, inaccurate diagnosis or drug resistance and toxicity. Thus, the discovery of new functional molecules will be important for the development of novel anti-cestode strategies. During the process of parasitic infection, the parasite-derived proteases are implicated as key factors for physiological functions and the pathogenicity of parasites, such as protein catabolism, nutrient acquisition, migration, tissue invasion, immune evasion and survival in the host. These proteases have been exploited as drug targets, vaccine candidates and serodiagnostic markers of controlling various parasite infections (McKerrow et al., 2006, Rascon and McKerrow, 2013, Tsubokawa et al., 2017, Yang et al., 2015). Leucine aminopeptidases (LAP, EC: 3.4.11.1) are a group of diverse and ubiquitous metalloexopeptidases, which belong to the peptidase M1 or M17 families. The enzyme performs proteolytic activities by preferentially catalyzing the removal of N-terminal leucine residues from polypeptide or protein substrates (Rawlings and Barrett, 1995, Rawlings et al., 2010). LAP functions presumably are involved in the processing, catabolism, degradation and regular turnover of intracellular proteins (Taylor, 1993). In structure, M17LAP consists of six identical monomers that form a hexamer. Each monomer possessed two divalent metal ions in its active site, but absent the specific motif “HEXXH” of M1LAPs (Burley et al., 1990, Matsui et al., 2006). Recently, many studies have identified M17LAPs as attractive proteins with diverse functions in parasites. In protozoan parasites, M17LAPs serve as regulators for free amino acid (Cadavid-Restrepo et al., 2011, Jia et al., 2010, Kang et al., 2011, Stack et al., 2007). In trematodes, M17LAPs have been found to be involved in invasion, egg hatching and digestion for fluke survival in the host (Acosta et al., 2008, Maggioli et al., 2011, McCarthy et al., 2004, Rinaldi et al., 2009). LAPs also work in encystation of Acanthamoeba castellanii (Lee et al., 2015). M17LAPs have been viewed as to be promising chemotherapeutic drug targets for the development of anti-parasite drugs based on their versatile functions in parasite biology.