TAURINE IN MARINE INVERTEBRATES
223
that cystine was formed by bacteria in the gut. Machlin el al. (1953)
administered S35 labelled sulphate to hens and recovered labelled
cystine from their eggs, methionine remaining unlabelled. Machin et al.
(1955) later injected S35 labelled sulphate into chick embryos and found
that all the S35 bound in organic material was incorporated into taurine.
Lowe and Roberts (1966) repeated this work with a similar result,
cystine, cysteic acid and methionine remaining unlabelled. Their
chromatograms also showed the formation of a possible precursor of
taurine. This did not react with ninhydrin and they did not identify
the substance. Yet another spot not reactive to ninhydrin appeared
much later on their chromatograms and this they hint might possibly
be 2-hydroxyethanesulphinic acid (isethionic acid) which Koechlin
(1954a and b, 1955) had identified a year earlier as being present in
large quantities in the axoplasm of the giant nerve fibres of squid.
Martin et al. (1966) and Miraglia et al. (1966) kept chicks on a basal diet
low in sulphate for 14 days and then added S35 sulphate to their diet.
The labelled sulphur became incorporated into taurine and taurocholate. On addition of inorganic sulphur compounds the proportion
of radioactive sulphur incorporated into taurine increased, possibly
indicating that there is an optimal substrate sulphur level. Addition
of glycine to the basal diet also gave an increased rate of taurinc synthesis. Methionine, cystine or cysteic acid showed little radioactivity.
Following the accumulation of labelled taurine in the liver there was an
increase in a substance which had the same Rf value as isothionic acid.
Chick liver, heart, spleen and kidney can actively convert taurine to this
acid. Under some dietary conditions a spot was found on the chromatograms having an Rf value of mercaptoethylamine and another of
lesser activity identified with hypotaurine. Martin et al. (1966) suggest
that, as in some bacteria, the formation of taurine from sulphate may
be mediated by the cysteine level and involve enzyme repression or
feedback, which might suggest that cysteine could be formed from
taurine.
All the above experiments indicate that vertebrates readily synthesize taurine using inorganic sulphate sulphur. Jacobsen and Smith
(1968) suggest that the conversion of inorganic sulphate to taurine is
carried out in three stages : (1) the reduction of sulphate to sulphite ;
(2) the fixation of sulphite to a 3 carbon aminated molecule derived
from L-cysteine leading to the formation of L-cysteic acid (the enzyme
involved, cysteinelyase, requires pyridoxine and probably breaks the
CS bond of the 8-carbon of cysteine with the formation of an intermediate, possibly a-aminoacrylic acid) ; (3) the decarboxylation of
cysteic acid t o form taurine. This pathway may be restricted to the
223
that cystine was formed by bacteria in the gut. Machlin el al. (1953)
administered S35 labelled sulphate to hens and recovered labelled
cystine from their eggs, methionine remaining unlabelled. Machin et al.
(1955) later injected S35 labelled sulphate into chick embryos and found
that all the S35 bound in organic material was incorporated into taurine.
Lowe and Roberts (1966) repeated this work with a similar result,
cystine, cysteic acid and methionine remaining unlabelled. Their
chromatograms also showed the formation of a possible precursor of
taurine. This did not react with ninhydrin and they did not identify
the substance. Yet another spot not reactive to ninhydrin appeared
much later on their chromatograms and this they hint might possibly
be 2-hydroxyethanesulphinic acid (isethionic acid) which Koechlin
(1954a and b, 1955) had identified a year earlier as being present in
large quantities in the axoplasm of the giant nerve fibres of squid.
Martin et al. (1966) and Miraglia et al. (1966) kept chicks on a basal diet
low in sulphate for 14 days and then added S35 sulphate to their diet.
The labelled sulphur became incorporated into taurine and taurocholate. On addition of inorganic sulphur compounds the proportion
of radioactive sulphur incorporated into taurine increased, possibly
indicating that there is an optimal substrate sulphur level. Addition
of glycine to the basal diet also gave an increased rate of taurinc synthesis. Methionine, cystine or cysteic acid showed little radioactivity.
Following the accumulation of labelled taurine in the liver there was an
increase in a substance which had the same Rf value as isothionic acid.
Chick liver, heart, spleen and kidney can actively convert taurine to this
acid. Under some dietary conditions a spot was found on the chromatograms having an Rf value of mercaptoethylamine and another of
lesser activity identified with hypotaurine. Martin et al. (1966) suggest
that, as in some bacteria, the formation of taurine from sulphate may
be mediated by the cysteine level and involve enzyme repression or
feedback, which might suggest that cysteine could be formed from
taurine.
All the above experiments indicate that vertebrates readily synthesize taurine using inorganic sulphate sulphur. Jacobsen and Smith
(1968) suggest that the conversion of inorganic sulphate to taurine is
carried out in three stages : (1) the reduction of sulphate to sulphite ;
(2) the fixation of sulphite to a 3 carbon aminated molecule derived
from L-cysteine leading to the formation of L-cysteic acid (the enzyme
involved, cysteinelyase, requires pyridoxine and probably breaks the
CS bond of the 8-carbon of cysteine with the formation of an intermediate, possibly a-aminoacrylic acid) ; (3) the decarboxylation of
cysteic acid t o form taurine. This pathway may be restricted to the