Fig. 5. Cellular localization of phospho-PKC substrates. Sea urchin spermatozoa were mechanically separated into heads and flagella and then detergent fractionated with Triton X-100. The soluble phospho-PKC substrate proteins of spermatozoa, as detected with an anti-phospho-PKC substrate antibody, were predominantly found in the sperm heads while those recovered in the Triton X-100-insoluble sperm fraction were mainly associated with the flagella. The arrowheads indicate the position of the 200, 100, 65 and 28 kDa bands. i, immotile; m, motile; sol, Triton X-100 soluble; insol, Triton X-100 insoluble. A blot representative of two other blots is presented.