240
f. A. ALLEN AND M. R. GARRET"
did suggest that the lower levels in Limulus as compared with Cancer
and Homarus is but a reflection of its evolutionary history and development. Only Hillman (1964, 1966) has compared the taurine content of
populations of the same species, in this case Crassostreu virginica
(Gmelin). He compared the taurine levels in addudor muscles of specimens from three populations from different salinity regimes, which he
kept in varying experimental salinities. Thus specimens from high
salinity environment (28%,) always had a higher taurine content than
those from a low (lo%,) irrespective of the experimental salinity in
which they were both kept. However, those from intermediate environmental salinities, and which showed intermediate values at high
experimental salinities, a t an experimental salinity of 12%, had a
taurine concentration equal to that of the population from the high
salinity environment under similar experimental conditions. Apart
from deducing an osmoregulatory role Hillman ( 1966) considered these
differences t o be physiological manifestations of genetic differences
among allopatric populations which have adapted their osmoregulatory
mechanisms to various salinity regimes.
IV. SUMMARY AND CONCLUSIONS
Taurine is not only an oxidative end product but also a key intermediate of sulphur metabolism. In marine invertebrates it appears to
have three organic functions. The best documented is its function in
intracellular isosmotic regulation where it (and " non-essential ') aminoacids) are preferentially lost when the salt concentration outside the
cell is lowered (p. 233 et seq.). It should be pointed out that at all times
the taurine concentration is low in the haemolymph (e.g., Kermack
et al., 1955; Allen, personal observations). It can be shown that specimens of Mya subjected to low salinities greatly increase the rate of loss
of ammonia from their bodies (Allen and Garrett, 1971). However, no
comparable increase occurs in excreted sulphate ions, which might be
expected from the degradation of taurine, nor in taurine itself. Thus, it
could be that sulphate ions are retained in the body or possibly might be
attached to mucopolysaccharides and disposed of by enhanced mucus
secretion. The other known functions are concerned with transphosphorylation, this particularly in marine polychaetes (p. 225), and with
the rate of transmission of nerve impulses (p. 230) and the ionic balance
of nerve axoplasm. In connection with the latter function it should be
pointed out that the ventral nerve cord of the lobster can fix C1402 and
that labelling occurs in taurine and in aspartic and glutamic acids
(Schoffeniels, 1968 ; Florkin and Schoffeniels, 1969). Experiments using
glucose-U-14C indicates that in the case of rtlanine, serine and glycine
f. A. ALLEN AND M. R. GARRET"
did suggest that the lower levels in Limulus as compared with Cancer
and Homarus is but a reflection of its evolutionary history and development. Only Hillman (1964, 1966) has compared the taurine content of
populations of the same species, in this case Crassostreu virginica
(Gmelin). He compared the taurine levels in addudor muscles of specimens from three populations from different salinity regimes, which he
kept in varying experimental salinities. Thus specimens from high
salinity environment (28%,) always had a higher taurine content than
those from a low (lo%,) irrespective of the experimental salinity in
which they were both kept. However, those from intermediate environmental salinities, and which showed intermediate values at high
experimental salinities, a t an experimental salinity of 12%, had a
taurine concentration equal to that of the population from the high
salinity environment under similar experimental conditions. Apart
from deducing an osmoregulatory role Hillman ( 1966) considered these
differences t o be physiological manifestations of genetic differences
among allopatric populations which have adapted their osmoregulatory
mechanisms to various salinity regimes.
IV. SUMMARY AND CONCLUSIONS
Taurine is not only an oxidative end product but also a key intermediate of sulphur metabolism. In marine invertebrates it appears to
have three organic functions. The best documented is its function in
intracellular isosmotic regulation where it (and " non-essential ') aminoacids) are preferentially lost when the salt concentration outside the
cell is lowered (p. 233 et seq.). It should be pointed out that at all times
the taurine concentration is low in the haemolymph (e.g., Kermack
et al., 1955; Allen, personal observations). It can be shown that specimens of Mya subjected to low salinities greatly increase the rate of loss
of ammonia from their bodies (Allen and Garrett, 1971). However, no
comparable increase occurs in excreted sulphate ions, which might be
expected from the degradation of taurine, nor in taurine itself. Thus, it
could be that sulphate ions are retained in the body or possibly might be
attached to mucopolysaccharides and disposed of by enhanced mucus
secretion. The other known functions are concerned with transphosphorylation, this particularly in marine polychaetes (p. 225), and with
the rate of transmission of nerve impulses (p. 230) and the ionic balance
of nerve axoplasm. In connection with the latter function it should be
pointed out that the ventral nerve cord of the lobster can fix C1402 and
that labelling occurs in taurine and in aspartic and glutamic acids
(Schoffeniels, 1968 ; Florkin and Schoffeniels, 1969). Experiments using
glucose-U-14C indicates that in the case of rtlanine, serine and glycine