In spite of its inherent physiological importance, studies on the occurrence, characteristics, and modulation of amylase in euryhaline crabs are lacking. We investigated the occurrence of amylase forms and the effect of acclimation to different salinities on their number and made a partial purification and characterization of the major form present in the hepatopancreas of Neohelice 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 between 30 and 40 °C; maintained at high NaCl concentrations (up to 4 M); increased by 5 mM K+, Li+, Co2+, and Mg2+ (36%-45%); inhibited by Cu2+, Zn2+, Cd2+, Fe2+, and Mn2+ (92.4% and 23.7%); not affected by Ni2+ or Ba2+; and enhanced almost 100% by Ca2+. Amylase exhibited Michaelis-Menten kinetics (starch: Km = 1.24 mg mL-1; glycogen: Km = 16.19 mg mL-1). The potential physiological significance and relationship to habitat conditions of the extra form in low salinity and the biochemical characteristics of the partially purified amylolytic activity (halotolerant, differential sensitivity to ions, capability to hydrolyze starch and glycogen) are discussed. [ABSTRACT FROM AUTHOR]