Multiple forms of lysozyme in copper stressed mussels (Mytilus edulis)

In a previous study we monitored fluctuations in the concentration of lysozyme in the hemolymph of copper stressed bay mussels, Mytilus edulis, concurrently by measuring enzymatic activity and by an enzyme-linked immunosorbent assay (ELISA).¹ In a number of instances the data collected by the two techniques from copper stressed mussels yielded contradictory results. In these instances the quantity of lysozyme, determined enzymatically, was significantly greater than the quantities determined by ELISA. These results prompted subsequent investigation into the cause of the discrepancies. In the course of the study a high molecular weight protein fraction (35 000 MW) from mussel hemocytes was isolated. Decreasing the ionic strength and concentration of the fraction caused dissociation into a 14 600 MW fraction characteristically identical to lysozyme.² Association to the 35 000 MW form is reversible upon an increase in ionic strength and concentration, and is presumed to be a dimer of lysozyme.^3,4 The ionic strength and pH optima for hydrolysis of suspensions of Micrococcus luteus were determined for the dimer. Polyclonal anti-lysozyme gammaglobulin preparations¹ were used in determinations of the relative immunological reactivity of various lysozyme preparations by immunodiffusion.⁵ The monomer form was more favorably precipitated or detectable than the lysozyme in hemocytes. disturbed hemocytes indicate an apparent increase in the extracellular concentration of the dimer as a result of cell damage. The observed low immunological reactivity would allow for the lack of detection by ELISA, and may have interfered with antibody-monomer interactions.