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J. A. ALLEN AND M. R. GARRETT
acid to hypotaurine with subsequent oxidation of the latter. Thoai
et al. (1963) also reported the conversion of S35 cysteine to hypotaurine
in Areiticolu, but they did not say whether radioactive cysteine sulphinic
acid or cysteic acid were present. It should. be noted that Robin and
Roche (1954) investigated several coelenterates and sponges and observed that taurine and hypotaurine always occur together. Shibuya
and Ouchi (1957) found hypotaurine in every tissue of the mollusc
Septifer and it has been reported from other molluscs (Ouchi 1959,
Tanaka, 1960).
Awapara (1962) was able to oxidize hypotaurine to taurine i n vitro
using fresh whole homogenates and soluble enzyme extracts of
Arenicola cristnta. However, the reaction appeared to be non-enzymatic as it was not hindered by prolonged boiling and although the
presence of worm homogenate or extract was necessary for the reaction
they suggest a metal ion may be acting as the catalyst.
Earlier, Schoberl (1933) had suggested that the conversion of
cysteine to taurine might be by way of cystamine. The existence of
another route to hypotaurine from cysteine or cystine was again suggested by Eldjarn (1954a and b) and Eldjarn and Pihl (1956) and by
Cavallini (1966) and Cavallini et al. (1955) when they found more
hypotaurine in the urine of the rat after feeding or injecting cystine or
cysteine, than if cysteine sulphinic acid was fed or injected. Thus,
although cystcine sulphinic acid is generally accepted as a precursor of
hypotaurine they found that it was only converted in part to hypotaurine. These authors also found cystamine disulphoxide in the urine
of rats fed cystine. Although this is known to be a product of hypotaurine under certain conditions, they suggested, as did Medes and
Floyd (1942), that it too might be an intermediate in the cystine-hypotaurine pathway. Eventually, Cavallini et al. (1963, 1966) showed that
an alternative enzymatic pathway does exist. The purified enzyme
showed specificity towards cystamine, and under conditions in which
the latter substance is oxidized to hypotaurine, cysteine and cystine
derivatives are not oxidized to a level higher than that of a disulphide.
The authors are of the opinion that cystamine (and cysteamine) could
be the preferential intermediates compared with cysteine sulphinic
acid in the route from cystine to hypotaurine and taurine, particularly
as it has been shown that this enzyme is widespread in animal tissues
(DuprB and De Marco, 1964). In fact, DuprB and Dc Marco (1964) also
had predicted this pathway.
The presence of thiotaurine in the urine of rats fed with L-cysteine
also gives indirect evidence of this pathway (Cavallini et al., 1959, 1960;
Mondovi and Tentori, 1961). The conversion of cystamine to hypo-
J. A. ALLEN AND M. R. GARRETT
acid to hypotaurine with subsequent oxidation of the latter. Thoai
et al. (1963) also reported the conversion of S35 cysteine to hypotaurine
in Areiticolu, but they did not say whether radioactive cysteine sulphinic
acid or cysteic acid were present. It should. be noted that Robin and
Roche (1954) investigated several coelenterates and sponges and observed that taurine and hypotaurine always occur together. Shibuya
and Ouchi (1957) found hypotaurine in every tissue of the mollusc
Septifer and it has been reported from other molluscs (Ouchi 1959,
Tanaka, 1960).
Awapara (1962) was able to oxidize hypotaurine to taurine i n vitro
using fresh whole homogenates and soluble enzyme extracts of
Arenicola cristnta. However, the reaction appeared to be non-enzymatic as it was not hindered by prolonged boiling and although the
presence of worm homogenate or extract was necessary for the reaction
they suggest a metal ion may be acting as the catalyst.
Earlier, Schoberl (1933) had suggested that the conversion of
cysteine to taurine might be by way of cystamine. The existence of
another route to hypotaurine from cysteine or cystine was again suggested by Eldjarn (1954a and b) and Eldjarn and Pihl (1956) and by
Cavallini (1966) and Cavallini et al. (1955) when they found more
hypotaurine in the urine of the rat after feeding or injecting cystine or
cysteine, than if cysteine sulphinic acid was fed or injected. Thus,
although cystcine sulphinic acid is generally accepted as a precursor of
hypotaurine they found that it was only converted in part to hypotaurine. These authors also found cystamine disulphoxide in the urine
of rats fed cystine. Although this is known to be a product of hypotaurine under certain conditions, they suggested, as did Medes and
Floyd (1942), that it too might be an intermediate in the cystine-hypotaurine pathway. Eventually, Cavallini et al. (1963, 1966) showed that
an alternative enzymatic pathway does exist. The purified enzyme
showed specificity towards cystamine, and under conditions in which
the latter substance is oxidized to hypotaurine, cysteine and cystine
derivatives are not oxidized to a level higher than that of a disulphide.
The authors are of the opinion that cystamine (and cysteamine) could
be the preferential intermediates compared with cysteine sulphinic
acid in the route from cystine to hypotaurine and taurine, particularly
as it has been shown that this enzyme is widespread in animal tissues
(DuprB and De Marco, 1964). In fact, DuprB and Dc Marco (1964) also
had predicted this pathway.
The presence of thiotaurine in the urine of rats fed with L-cysteine
also gives indirect evidence of this pathway (Cavallini et al., 1959, 1960;
Mondovi and Tentori, 1961). The conversion of cystamine to hypo-