The interaction of seminalplasmin with chlortetracycline, a fluorescent chelate probe of Ca2+, was studied. The results indicate that seminalplasmin binds to chlortetracycline. The binding is not influenced by salt. Both Ca2+ and seminalplasmin probably bind to the same site on chlortetracycline. Seminalplasmin also reduced the Tb3+-associated fluorescence of bovine spermatozoal plasma membrane. These results are discussed in relation to the inhibitory effect of seminalplasmin on the uptake of Ca2+ in bovine spermatozoa.
