218
J. A. ALLEN AND M. R. GARRETT
plained in terms of the abnormally large doses used in experiments
iu vilro. No cystcic acid was found in the liver of rats in injection
experiments with small amounts of cysteine S3=. However, cysteic acid
injected in large quantities results in the formation of taurine. Thus the
organism may be capable of oxidizing eysteine to cysteic acid and then
decnrboxylnting tlic latter to taurine but only as an alternative pathway. Awapara and Wingo (1 983) assume that taurinc! is formed froin
hypotaurinc by oxid. d t' 1011.
The resiilts of Blaschko et al. (1963) at first sccmcd to contradict the
theory that the normal pathway from cysteine to taurine is via the intermediate hypotaurine when they found that pyridoxine* deficient rats
did not excrete tauriiie (although this was proved later not to be a total
loss) and at the same time thcy could find no cvidencc of cysteic acid
decarboxylase activity in the liver. Yet Fromageot (1951), who found
that in Vitamin B,* deficiency taurine and hypotaurine are absent
from urine, also demonstrated in vitro that decarboxylation of cysteine
sulphinic acid had been suppressed. This was latcr confirmed by
Chatagner et al. (1964). To explain the apparent discrepancy of the
previous results, Blasehko and Hopc (1954) repeated the suggestion of
Awapara and IVingo (1953) that some pyridoxine " requiring " enzyme
is responsible both for the decarboxylation of cysteie acid and of cysteinc
sulphinic acid. Strong support for this view came when Hope (1956)
found that liver extract from dogs, rats and other mammals could
decarboxylate both L-cystcic acid and L-cysteine sulphiiiic acid
although the rate of decarboxylation of thc sulphinic acid was greatcr
than tlie cysteie acid. However, high decarboxylation activity with one
substrate was always linked with high activity in the other and in
animals such as thc cat where thcrc is no decarboxylation of ~-cysteic
acid, there is no drcarboxylation of L-cystehe sulphinic acid either.
While the rcsults explain why L-cysteic acid can act as a. precursor of
tauriiie, it seems likcly that r,-cysteine sulphinic acid is the chicf
substrate for the enzyme, and is the preferred pathway for taurine
formation.
Bergerct et al. (1958) and Jacobsen et al. (1964) found that the
decarboxylase of tlie brain of the rat differed from that of the liver.
Brain decarboxylasc is unaffected by Vitamin Be deficiency while that
of the liver is entirely suppressed. Hope (1957) similarly found the
amount of taurine in the brain to be unaffected by pyridoxine deficiency
Pyridoxal phosphate, cofactor in decarboxylaso activity, is the prccursor of
pyridoxine. Vitamin B, comprisos a family of substances structurally rolated to pyridoxal phosphate and presumably Ba doficiency has the same effect as pyridoxine
deficiency (see Jacobsen and Smith, 1968).
J. A. ALLEN AND M. R. GARRETT
plained in terms of the abnormally large doses used in experiments
iu vilro. No cystcic acid was found in the liver of rats in injection
experiments with small amounts of cysteine S3=. However, cysteic acid
injected in large quantities results in the formation of taurine. Thus the
organism may be capable of oxidizing eysteine to cysteic acid and then
decnrboxylnting tlic latter to taurine but only as an alternative pathway. Awapara and Wingo (1 983) assume that taurinc! is formed froin
hypotaurinc by oxid. d t' 1011.
The resiilts of Blaschko et al. (1963) at first sccmcd to contradict the
theory that the normal pathway from cysteine to taurine is via the intermediate hypotaurine when they found that pyridoxine* deficient rats
did not excrete tauriiie (although this was proved later not to be a total
loss) and at the same time thcy could find no cvidencc of cysteic acid
decarboxylase activity in the liver. Yet Fromageot (1951), who found
that in Vitamin B,* deficiency taurine and hypotaurine are absent
from urine, also demonstrated in vitro that decarboxylation of cysteine
sulphinic acid had been suppressed. This was latcr confirmed by
Chatagner et al. (1964). To explain the apparent discrepancy of the
previous results, Blasehko and Hopc (1954) repeated the suggestion of
Awapara and IVingo (1953) that some pyridoxine " requiring " enzyme
is responsible both for the decarboxylation of cysteie acid and of cysteinc
sulphinic acid. Strong support for this view came when Hope (1956)
found that liver extract from dogs, rats and other mammals could
decarboxylate both L-cystcic acid and L-cysteine sulphiiiic acid
although the rate of decarboxylation of thc sulphinic acid was greatcr
than tlie cysteie acid. However, high decarboxylation activity with one
substrate was always linked with high activity in the other and in
animals such as thc cat where thcrc is no decarboxylation of ~-cysteic
acid, there is no drcarboxylation of L-cystehe sulphinic acid either.
While the rcsults explain why L-cysteic acid can act as a. precursor of
tauriiie, it seems likcly that r,-cysteine sulphinic acid is the chicf
substrate for the enzyme, and is the preferred pathway for taurine
formation.
Bergerct et al. (1958) and Jacobsen et al. (1964) found that the
decarboxylase of tlie brain of the rat differed from that of the liver.
Brain decarboxylasc is unaffected by Vitamin Be deficiency while that
of the liver is entirely suppressed. Hope (1957) similarly found the
amount of taurine in the brain to be unaffected by pyridoxine deficiency
Pyridoxal phosphate, cofactor in decarboxylaso activity, is the prccursor of
pyridoxine. Vitamin B, comprisos a family of substances structurally rolated to pyridoxal phosphate and presumably Ba doficiency has the same effect as pyridoxine
deficiency (see Jacobsen and Smith, 1968).