why iodonation done at high temperature
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The reports of Ludwig and von Mutzenbecher (1) and Harington and
Rivers (2) established the fact that thyroxine can be isolated from hydroly-
sates of iodinated proteins prepared under rather closely defined con-
ditions. Little attention was given, however, to the thyroidal effects
to be obtained without preliminary hydrolysis of the iodinated proteins used.
Thyroidal responses indicating a relatively low order of potency were re-
ported for degradation products of iodinated serum albumin by Salter and
Lerman (3). Similar effects were obtained by oral administration of iodi-
nated serum albumin itself by Lerman and Salter (4).
In our early experiments it was found that iodinated casein prepared in a
medium buffered with sodium bicarbonate exerted thyroidal effects when
given either orally or by injection. It was demonstrated (5) that, other
conditions being held constant, the thyroidal activity of iodinated casein
increases progressively with increasing additions of iodine until sufficient
iodine has been added to combine 2 atoms per molecule of tyrosine in the
protein. Iodination beyond this point results in a significant loss of thyroi-
da1 activity.
In extensive experiments that are being published elsewhere (6), it was
found that, if the iodine input was held constant, and the bicarbonate con-
centration of the reaction mixture was varied, the attainment of maximal
thyroidal activity was dependent upon adding sufficient bicarbonate to
hold the pH within the range of approximately 6.8 to 8.0. Addition of
insufficient bicarbonate resulted in products with low activity; the use of an
excess of bicarbonate appeared to have no effect on the result, however.
All of the reactions up to this point had been conducted at the usual tem-
perature of 38”. When the concentrations of both the iodine and the sodium
bicarbonate were held within the optimal ranges thus established, it was
found (6) that about a 4-fold increase in thyroidal activity could be obtained
by incubating the preparations at an elevated temperature of GO-70”.
Furthermore, this increase would takn place whether the protein was first.
Rivers (2) established the fact that thyroxine can be isolated from hydroly-
sates of iodinated proteins prepared under rather closely defined con-
ditions. Little attention was given, however, to the thyroidal effects
to be obtained without preliminary hydrolysis of the iodinated proteins used.
Thyroidal responses indicating a relatively low order of potency were re-
ported for degradation products of iodinated serum albumin by Salter and
Lerman (3). Similar effects were obtained by oral administration of iodi-
nated serum albumin itself by Lerman and Salter (4).
In our early experiments it was found that iodinated casein prepared in a
medium buffered with sodium bicarbonate exerted thyroidal effects when
given either orally or by injection. It was demonstrated (5) that, other
conditions being held constant, the thyroidal activity of iodinated casein
increases progressively with increasing additions of iodine until sufficient
iodine has been added to combine 2 atoms per molecule of tyrosine in the
protein. Iodination beyond this point results in a significant loss of thyroi-
da1 activity.
In extensive experiments that are being published elsewhere (6), it was
found that, if the iodine input was held constant, and the bicarbonate con-
centration of the reaction mixture was varied, the attainment of maximal
thyroidal activity was dependent upon adding sufficient bicarbonate to
hold the pH within the range of approximately 6.8 to 8.0. Addition of
insufficient bicarbonate resulted in products with low activity; the use of an
excess of bicarbonate appeared to have no effect on the result, however.
All of the reactions up to this point had been conducted at the usual tem-
perature of 38”. When the concentrations of both the iodine and the sodium
bicarbonate were held within the optimal ranges thus established, it was
found (6) that about a 4-fold increase in thyroidal activity could be obtained
by incubating the preparations at an elevated temperature of GO-70”.
Furthermore, this increase would takn place whether the protein was first.
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