Amylase in the hepatopancreas of a euryhaline burrowing crab: characteristics and modulation

Abstract

In spite of its inherent physiological importance, studies on the occurrence, characteristics, and modulation of amylase ineuryhaline crabs are lacking. We investigated the occurrence of amylase forms and the effect of acclimation to different salinities on theirnumber and made a partial purification and characterization of the major form present in the hepatopancreas ofNeohelice granulata .Zymogram analysis revealed 5 amylase forms in crabs acclimated to 35 psu (seawater) and 37 psu, and an additional band at 10 psu,but with a major form (29 kDa) in all cases, which was partially purified and characterized. Amylolytic activity was maximal between30 and 40 °C; maintained at high NaCl concentrations (up to 4 M); increased by 5 mM K + , Li + , Co 2+ , and Mg 2+(36% 45%); inhibited byCu 2+ , Zn 2+ , Cd 2+ , Fe 2+ , and Mn 2+(92.4% and 23.7%); not affected by Ni 2+or Ba 2+ ; and enhanced almost 100% by Ca 2+ . Amylase exhibitedMichaelis Menten kinetics (starch: K m= 1.24 mg mL1 ; glycogen: K m= 16.19 mg mL1 ). The potential physiological significance andrelationship to habitat conditions of the extra form in low salinity and the biochemical characteristics of the partially purified amylolyticactivity (halotolerant, differential sensitivity to ions, capability to hydrolyze starch and glycogen) are discussed.