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One of the essential steps in canine parvovirus (CPV) infection, the release from endosomal vesicles, is dominated by interactions between the virus capsid and the endosomal membranes. In this study, the effect of sphingomyelin and phosphatidyl serine on canine parvovirus capsid and on the phospholipase A(2) (PLA(2)) activity of CPV VP1 unique N-terminus was analyzed. Accordingly, a significant (P< or =0.05) shift of tryptophan fluorescence emission peak was detected at pH 5.5 in the presence of sphingomyelin, whereas at pH 7.4 a similar but minor shift was observed. This effect may relate to the exposure of VP1 N-terminus in acidic pH as well as to interactions between sphingomyelin and CPV. When the phenomenon was further characterized using circular dichroism spectroscopy, differences in CPV capsid CD spectra with and without sphingomyelin and phosphatidyl serine were detected, corresponding to data obtained with tryptophan fluorescence. However, when the enzymatic activity of CPV PLA(2) was tested in the presence of sphingomyelin, no significant effect in the function of the enzyme was detected. Thus, the structural changes observed with spectroscopic techniques appear not to manipulate the activity of CPV PLA(2), and may therefore implicate alternative interactions between CPV capsid and sphingomyelin.