222
J. A. G E N AND Y. R. GARRETT
new enzyme or enzyme system present that catalyses the oxidation of
cysteamine to taurine directly and not via hypotaurine. This is not
necessarily significant if oxidation is non-enzymatic (Abbott and
Awapara, 1960). Other authors have failed to convert hypotauriiie to
taurine in vitro (Jacobsen and Smith, 1968).
Allen and Awapara (1960) showed that Rangia cuneuta Gray, a
freshwater bivalve normally containing no taurine, could synthesize
taurine from injected S35 methionine via the oxidation of cysteine
sulphinic acid to cysteic acid followed by decarboxylation of the latter
to form taurine and with some production of labelled sulphate. Taurine
is excreted by Rangia as soon as it is formed. Note, this sequence is
regarded as a secondary pathway in vertebrates. In parallel experiments
using Nytilus edulis LinnB, they found 24 h after the injection of S35
methioniiie, labelled hypotaurine and taurine to be present, but only
in small quantities. Formation of taurine in this animal, which normally contains large amounts of the substance, is a slow process. In
addition, in the Mytilus experiments, Allen and Awapara (1960)
recorded labelled cystathionine, an unknown compound which they
thought possibly to be methionine sulphate, together with a relatively
small amount of cystine/cysteine. These additional results together
with those obtained invitro by Yoneda (1968) indicate that the pathway
via cysteamine suggested by Cavallini et al. (1955) may exist in Mytilus.
However, the fact that in experiments using cysteamine, taurine
formation in vivo is a slow process (much slower than found in vitro)
and that cysteamine is not readily identified as being present in the
animal suggests that it is more likely that cysteine sulphinic acid is the
intermediate, and that the low rate of taurine synthesis in Mytilus
prevented Allen and Awapara (1960) from identifying it. Curiously in
Mya, injected S35 methionine is metabolized at a very high rate. There
is a high yield of taurine, up to 50% of recovered activity, within the
first hour. The taurine is also subject to a high rate of turnover,
50% being converted to other substances within 15 h (Allen, personal
observations).
There is some evidence that other pathways may exist for the
formation of taurine. Thus, sulphate sulphur may be incoporated into
taurine. Jacobsen and Smith (1968) point out that xenic cockroaches
possess all the necessary chemical steps. Bostr6m and Aqvist (1952)
injected rats interperitoneally with the sodium sulphate labelled with S35
and isolated labelled taurine from the liver after 2 h and recorded the
maximum concentrations after 8 h. In addition very small amounts
of labelled methionine and cystine were found in the liver after 24 h.
This was confirmed by Dziewiatkowski (1954) who, however, believed
J. A. G E N AND Y. R. GARRETT
new enzyme or enzyme system present that catalyses the oxidation of
cysteamine to taurine directly and not via hypotaurine. This is not
necessarily significant if oxidation is non-enzymatic (Abbott and
Awapara, 1960). Other authors have failed to convert hypotauriiie to
taurine in vitro (Jacobsen and Smith, 1968).
Allen and Awapara (1960) showed that Rangia cuneuta Gray, a
freshwater bivalve normally containing no taurine, could synthesize
taurine from injected S35 methionine via the oxidation of cysteine
sulphinic acid to cysteic acid followed by decarboxylation of the latter
to form taurine and with some production of labelled sulphate. Taurine
is excreted by Rangia as soon as it is formed. Note, this sequence is
regarded as a secondary pathway in vertebrates. In parallel experiments
using Nytilus edulis LinnB, they found 24 h after the injection of S35
methioniiie, labelled hypotaurine and taurine to be present, but only
in small quantities. Formation of taurine in this animal, which normally contains large amounts of the substance, is a slow process. In
addition, in the Mytilus experiments, Allen and Awapara (1960)
recorded labelled cystathionine, an unknown compound which they
thought possibly to be methionine sulphate, together with a relatively
small amount of cystine/cysteine. These additional results together
with those obtained invitro by Yoneda (1968) indicate that the pathway
via cysteamine suggested by Cavallini et al. (1955) may exist in Mytilus.
However, the fact that in experiments using cysteamine, taurine
formation in vivo is a slow process (much slower than found in vitro)
and that cysteamine is not readily identified as being present in the
animal suggests that it is more likely that cysteine sulphinic acid is the
intermediate, and that the low rate of taurine synthesis in Mytilus
prevented Allen and Awapara (1960) from identifying it. Curiously in
Mya, injected S35 methionine is metabolized at a very high rate. There
is a high yield of taurine, up to 50% of recovered activity, within the
first hour. The taurine is also subject to a high rate of turnover,
50% being converted to other substances within 15 h (Allen, personal
observations).
There is some evidence that other pathways may exist for the
formation of taurine. Thus, sulphate sulphur may be incoporated into
taurine. Jacobsen and Smith (1968) point out that xenic cockroaches
possess all the necessary chemical steps. Bostr6m and Aqvist (1952)
injected rats interperitoneally with the sodium sulphate labelled with S35
and isolated labelled taurine from the liver after 2 h and recorded the
maximum concentrations after 8 h. In addition very small amounts
of labelled methionine and cystine were found in the liver after 24 h.
This was confirmed by Dziewiatkowski (1954) who, however, believed