of these proteins. Eotlotyrosiiic may dso condense to form iodothyronines the best known of which arc 3,5,3-tri-iodothyronine (T3)
and thyroxine (T,) which in vcrtebriite animals are normally bound by
peptide bonds in the protein tliyroglobulin but can be releaaed from it
by enzymatic action. 'l'ri-iodothyronine and thyroxin are the active
hormonal componeiit,~ of the vertebrate thyroid gland (Roche, 1959 ;
Berg et al., I959 ; Corbman, 1969).
In escidians orgcmically bound iodine has been found to occur in the
cuticle of the test, in the endostyle and to a lesser extent in the pharyngeal wall and in the blood. Iodine was first identified in the test of a
number of species of ascidians by Cameron ( 1 915) but it is only recently
with the introduction of radio-tracer techniques and chromatography
that it has been possible to localize and identify these substances.
According to Barrington (1957), Barrington and Barron (1960),
Barrington and Thorpe (1968), and Roche et al. (1962b) most of the
iodine in the test is to be found in the proteinaceous cuticle on the
outer surface where it is involved in the formation of a scleroprotein.
Barrington and Barron (1960) identified only DIT and T, in the test of
Ciona intestinalis, but later, using two-dimensional chromatography,
Barrington and Thorpe (1963, 1968) concluded that MIT and DIT
could be positively identified in the tests of Ciona and Dendrodoa
grossularia. In the latter species Amaral et al. (1972) have identified
MIT, DIT and T, but not T3. Roche and his co-workers (Roche et al.,
1960, 1962a,b, 1964) found that both T3 and T4 are present in hydrolysates of the test of Ciona intestinalis, although they conceded (Roche
et al., 1964) that these iotiothyronines may not be produced in situ
but may b(i transported from elsewtierfa in the body of the escidian.
There is indeed little reason to bdieve that the iodinated compounds
are acttially formed in the test. Salvatore ( 1 9(M) considered most
iodine binding occui*s in the test and riot elsewhere in the body. Roche
et al. (1963, 1964) found that iodinc uptake in Ciona was markedly
arrested following ri.movul of the tvst and on1,y resumed after new & A t
formation liad comtnenc.ed. This suggests that uptake of iodinc may
be a function of t,he amount of test material present, but or1 the other
hand autoradiographs (Kennedy, 1 966 ; Barrington and Thorpe, 1968)
show an active movement of iodine through the test substance and
toward the cuticle. Kennedy has also identified iodinated compounds
in the blood and it seems more likely that this is the site of iodine uptake
rather than that it should occur directly into the cuticle of the test.
The organic binding of iodine in the ascidian endostyle was first
demonstrated by Bwrington and Franchi (1 956) and has been followed
up in a series of papers by Barrington cmd his co-workers (Barrington,
and thyroxine (T,) which in vcrtebriite animals are normally bound by
peptide bonds in the protein tliyroglobulin but can be releaaed from it
by enzymatic action. 'l'ri-iodothyronine and thyroxin are the active
hormonal componeiit,~ of the vertebrate thyroid gland (Roche, 1959 ;
Berg et al., I959 ; Corbman, 1969).
In escidians orgcmically bound iodine has been found to occur in the
cuticle of the test, in the endostyle and to a lesser extent in the pharyngeal wall and in the blood. Iodine was first identified in the test of a
number of species of ascidians by Cameron ( 1 915) but it is only recently
with the introduction of radio-tracer techniques and chromatography
that it has been possible to localize and identify these substances.
According to Barrington (1957), Barrington and Barron (1960),
Barrington and Thorpe (1968), and Roche et al. (1962b) most of the
iodine in the test is to be found in the proteinaceous cuticle on the
outer surface where it is involved in the formation of a scleroprotein.
Barrington and Barron (1960) identified only DIT and T, in the test of
Ciona intestinalis, but later, using two-dimensional chromatography,
Barrington and Thorpe (1963, 1968) concluded that MIT and DIT
could be positively identified in the tests of Ciona and Dendrodoa
grossularia. In the latter species Amaral et al. (1972) have identified
MIT, DIT and T, but not T3. Roche and his co-workers (Roche et al.,
1960, 1962a,b, 1964) found that both T3 and T4 are present in hydrolysates of the test of Ciona intestinalis, although they conceded (Roche
et al., 1964) that these iotiothyronines may not be produced in situ
but may b(i transported from elsewtierfa in the body of the escidian.
There is indeed little reason to bdieve that the iodinated compounds
are acttially formed in the test. Salvatore ( 1 9(M) considered most
iodine binding occui*s in the test and riot elsewhere in the body. Roche
et al. (1963, 1964) found that iodinc uptake in Ciona was markedly
arrested following ri.movul of the tvst and on1,y resumed after new & A t
formation liad comtnenc.ed. This suggests that uptake of iodinc may
be a function of t,he amount of test material present, but or1 the other
hand autoradiographs (Kennedy, 1 966 ; Barrington and Thorpe, 1968)
show an active movement of iodine through the test substance and
toward the cuticle. Kennedy has also identified iodinated compounds
in the blood and it seems more likely that this is the site of iodine uptake
rather than that it should occur directly into the cuticle of the test.
The organic binding of iodine in the ascidian endostyle was first
demonstrated by Bwrington and Franchi (1 956) and has been followed
up in a series of papers by Barrington cmd his co-workers (Barrington,