The male reproductive system of the mollusc bivalve Unio elongatulus contains two distinct forms of alpha-L-fucosidase, one present in the gonad fluid and a second one associated with the sperm plasma membrane. Both activities were purified to homogeneity. The soluble seminal plasma enzyme had an oligomeric MW of 56 kDa as determined by MALDI-TOF mass spectrometry, whereas the enzyme purified from sperm plasma membranes had an MW of 68 kDa. Analyzed by lectin blotting with ConA and PNA, the 68 kDa enzyme did not bind either lectin, whereas the 56 kDa form bound ConA only. Both fucosidases followed a Michaelis-Menten kinetics with the K(m) of the sperm-bound enzyme being 7.1 x 10(-4) M and that of the seminal enzyme being 9.1 x 10(-4) M. Both had a pH optimum of 5.0.