Direct assay of bound sialic acids on rat spermatozoa from the caput and cauda epididymidis

Bound sialic acids on rat spermatozoa were assayed by oxidation with 1 mM-NaIO4 at 0 degree C, liberating C-9 as formaldehyde which was further quantitated using 3-methyl-2-benzothiazolinone. The mean +/- s.d. (n = 20) content of bound sialic acids of spermatozoa from the caput and cauda epididymidis was 50.9 +/- 8.0 and 25.2 +/- 3.8 nmol/10(8) spermatozoa respectively. About 85% of the former and 75% of the latter could be extracted by 1% Triton X-100 and 2 mM-dithiothreitol. About 70% of the former and 20% of the latter were released by neuraminidase from Vibrio cholerae. About 40% of the former and 30% of the latter were sensitive to trypsin. During sperm maturation, the decrease in the total bound sialic acids was due to the decrease in the neuraminidase-sensitive but not the neuraminidase-resistant sialic acids.