The Journal of Cell Biology, Vol 86, 417-423, Copyright © 1980 by The Rockefeller University Press
The localization of protein carboxyl-methylase in sperm tails
P Bouchard, C Gagnon, DM Phillips and CW Bardin
Protein carboxyl-methylase (PCM), an enzyme known to be involved in
exocytotic secretion and chemotaxis, has been studied in rat and rabbit
spermatozoa. PCM activity and its substrate methyl acceptor protein(s)
(MAP) were demonstrated in the supernate after solubilization of the sperm
cell membrane by detergent (Triton X-100). A protein methylesterase that
hydrolyzes methyl ester bonds created by PCM was demonstrated in rabbit but
not in rat spermatozoa. This enzyme was not solubilized by nonionic
detergent. The specific activities of PCM in rat spermatozoa from caput and
cauda epididymis were similar and lower than that found in testis. By
contrast, MAP substrates were low in testis and increased in parallel with
sperm maturation in the epididymis. Multiple MAP were demonstrated in
spermatozoa by polyacrylamide gel electrophoresis. The pattern of these
proteins was similar in spermatozoa from different portions of the
reproductive tract. Fractionation of heads and tails of rat spermatozoa on
sucrose gradients indicated that PCM was found exclusively in the tail
fraction, whereas MAP was detected both in head and tail fractions. The
presence of all the components of the protein carboxyl-methylation system
in spermatozoa and the localization of PCM and some of its substrates in
the sperm tail are consistent with their involvement in sperm cell
motility.
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