TAURINE IN MARINE INVERTEBRATES
239
acid (GABA), a specific inhibitor of impulse transmission in the central
nervous system. Taurine, too, inhibits transmission of nerve impulse
both in mammals (Curtis and Watkins, 1961) and in marine invertebrates (Dude1 et al., 1963; Kravitz et al., 1963a and b). The
inhibitory effect is much smaller than in the case of GABA (Kravitz
et al., 1963b ; Edwards and Kuffler, 1959). Similarly L-cysteic acid and
L-cysteine sulphinic acid, precursors of taurine, like glutamic acid, the
precursor of GABA, have an excitatory effect on impulse transmission,
but the content of taurine in motor and inhibitor axons is the same
(Kravitz et al., 1963a).
Recent work on marine algae does provide a hint of a further
possible function of taurine in marine invertebrates and molluscs in
particular. Taurine is mainly found in those marine algae which
contain relatively large amounts of polysaccharide sulphates (Schweiger,
1967). This had previously been noted by Lindberg (1955) and both
these authors take the view that the polysaccharide sulphates may be
formed from taurine via a transesterification reaction involving choline
sulphate. The same argument may be applied to marine bivalves and
gastropods, many functions of which depend on a copious supply of
sulphonated polysaccharides. The Mollusca, more than any other
phylum, are noted for their high taurine content (see p. 211).
Simpson et al. (1969) suggested the possibility that taurine is not
produced by invertebrates but acquired from their diet. While it is
undoubtedly true that marine invertebrates are capable of forming
taurine-these authors were sceptical even of this, reasoning from the
wide range of values in animals from the same environment-taurine
may well be obtained from their diet. Thus taurine is known to be
present in a wide range of algae (Table 111). It is present in only trace
quantities in sea water even though it is known to be excreted unchanged
by animals (Webb and Johannes, 1966, 1967). However, marine
bivalves, e.g., Mya and Tellina, can take up taurine out of solution
(Allen, personal observations). It is questionable whether quantities of
taurine present in food play anything more than a minor role in providing taurine. However, cysteinolic acid present in Ulva and Enteromorpha (Ito, 1963) and Polysiphonia (Wickberg, 1957) has been
reported in the gastropod Siphonaria zelandica, which has also a
rich taurine content (Bedford, 1969). A pathway from D-cysteinolic
ucid (2-~-amino-3-hydroxyl-l-propane sulphonic acid) to taurine, while
likely, has yet t o be reported.
Little work has been carried out to indicate the significance of the
different quantitiesof taurinepresent indifferent animalsof the same class,
for example, in the Annelida and in the Mollusca. Stevens et al. (1961)
239
acid (GABA), a specific inhibitor of impulse transmission in the central
nervous system. Taurine, too, inhibits transmission of nerve impulse
both in mammals (Curtis and Watkins, 1961) and in marine invertebrates (Dude1 et al., 1963; Kravitz et al., 1963a and b). The
inhibitory effect is much smaller than in the case of GABA (Kravitz
et al., 1963b ; Edwards and Kuffler, 1959). Similarly L-cysteic acid and
L-cysteine sulphinic acid, precursors of taurine, like glutamic acid, the
precursor of GABA, have an excitatory effect on impulse transmission,
but the content of taurine in motor and inhibitor axons is the same
(Kravitz et al., 1963a).
Recent work on marine algae does provide a hint of a further
possible function of taurine in marine invertebrates and molluscs in
particular. Taurine is mainly found in those marine algae which
contain relatively large amounts of polysaccharide sulphates (Schweiger,
1967). This had previously been noted by Lindberg (1955) and both
these authors take the view that the polysaccharide sulphates may be
formed from taurine via a transesterification reaction involving choline
sulphate. The same argument may be applied to marine bivalves and
gastropods, many functions of which depend on a copious supply of
sulphonated polysaccharides. The Mollusca, more than any other
phylum, are noted for their high taurine content (see p. 211).
Simpson et al. (1969) suggested the possibility that taurine is not
produced by invertebrates but acquired from their diet. While it is
undoubtedly true that marine invertebrates are capable of forming
taurine-these authors were sceptical even of this, reasoning from the
wide range of values in animals from the same environment-taurine
may well be obtained from their diet. Thus taurine is known to be
present in a wide range of algae (Table 111). It is present in only trace
quantities in sea water even though it is known to be excreted unchanged
by animals (Webb and Johannes, 1966, 1967). However, marine
bivalves, e.g., Mya and Tellina, can take up taurine out of solution
(Allen, personal observations). It is questionable whether quantities of
taurine present in food play anything more than a minor role in providing taurine. However, cysteinolic acid present in Ulva and Enteromorpha (Ito, 1963) and Polysiphonia (Wickberg, 1957) has been
reported in the gastropod Siphonaria zelandica, which has also a
rich taurine content (Bedford, 1969). A pathway from D-cysteinolic
ucid (2-~-amino-3-hydroxyl-l-propane sulphonic acid) to taurine, while
likely, has yet t o be reported.
Little work has been carried out to indicate the significance of the
different quantitiesof taurinepresent indifferent animalsof the same class,
for example, in the Annelida and in the Mollusca. Stevens et al. (1961)