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At limiting velocity 50 x 10(6) dead spermatozoa consumed 13.6 microliters O2/h and degraded 6.1 x 10(-7) mol L-phenylalanine/h. Substrate concentration in egg yolk was equivalent to 6.1 x 10(-3) M-L-phenylalanine. At a substrate concentration of 3 x 10(-2) M-L-phenylalanine, oxidase activity was significantly affected by oxygen tension (r = 0.947, P less than 0.01) and temperature (r = 0.995, P less than 0.01). Non-return rates were not affected when semen was stored at 5 degrees C in 20% egg yolk diluents with catalase but were significantly increased with semen stored at ambient temperatures of 15-23 degrees C.

Most (94%) of the aromatic L-amino acid oxidase activity in dead bovine spermatozoa was recovered in tail preparations. The enzyme was released from the cell in sodium citrate but not in sodium phosphate or sodium chloride solutions but oxidase activity was not significantly different in sodium phosphate or sodium citrate buffers (9.6 microliters O2/h and 11.2 microliters O2/h). The activity in ejaculated spermatozoa was correlated with the percentage of dead spermatozoa (r = 0.954, P less than 0.01) but could not be detected in freshly collected epididymal spermatozoa. Killed epididymal spermatozoa showed oxidase activity (10.1 microliters O2/h) similar to that of killed ejaculated spermatozoa (9.2 microliters O2/h). It is concluded that death of spermatozoa occurs in the ampulla and/or at ejaculation and that between-bull differences in the percentage of dead spermatozoa are a consequence of differences between bulls in conditions in the ampulla and/or at ejaculation.

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