Amylase, maltase and sucrase activities in hepatopancreas of the euryhaline crab Neohelice granulata (Decapoda: Brachyura: Varunidae): partial characterization and response to low environmental salinity

Abstract

Studies on digestive adjustments at the biochemical level in relation to salinity in euryhaline crabs are lacking. Moreover, knowledge of biochemical digestive characteristics of euryhaline crabs (i.e. occurrence and characteristics of key digestive enzyme activities) is still scarce and fragmentary. We studied the occurrence, characteristics and response to low salinity of amylase, maltase and sucrase activities in the hepatopancreas of the euryhaline crab Neohelice (Chasmagnathus) granulata. Maximal amylase and maltase activities were found at pH 5.2. Sucrase activity was maximal within the pH range 3.6-5.2. Amylase, maltase and sucrase activities showed a Michaelis-Menten kinetics (km = 0.41±0.10 mg ml -1; 1.37±1.03 mM and 0.55±0.45 mM, respectively). In crabs acclimated to low salinity (10 psu; hyperregulating conditions), amylase activity (7263±980 μg maltose min -1 mg prot -1) was higher than in 35 psu (osmoconforming conditions) (3605±340 μg maltose min -1 mg prot -1). Maltase and sucrase activities (497±98 and 64±16 μg glucose min -1 mg prot -1, respectively) were similar in both salinities. The response of amylase activity to low salinity suggests a role in digestive adjustments upon hyperregulation. This study contributes to a better understanding of the complexity of the biochemical adaptations to low salinity in euryhaline crabs.