AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 1 144-R149, Copyright © 1994 by American Physiological Society
Characterization and postnatal development of 5'-deiodinase activity in goat perirenal fat
F. Nicol, H. Lefranc, J. R. Arthur and P. Trayhurn
Division of Biochemical Sciences, Rowett Research Institute, Aberdeen, Scotland, United Kingdom.
The capacity to generate the active thyroid hormone 3,3',5-triiodothyronine
(T3) from thyroxine (T4) has been assessed in the major adipose tissue
depot (perirenal) of newborn goats through measurements of iodothyronine
5'-deiodinase activity. High activity of the enzyme was found in the
perirenal adipose tissue. Developmental studies demonstrated that there was
a rise, then a fall, in iodothyronine 5'-deiodinase activity (per milligram
of protein) over the first week of postnatal life, with a further decline
between the second and third weeks. At 3 wk of age, the activity per gram
of tissue was only 2% of that of the newborn; however, because of
age-related increases in the lipid content of the perirenal adipose tissue,
the activity per cell (per microgram of DNA) at 3 wk of age was
approximately 10% of the activity in the newborn. Kinetic studies and
inhibition characteristics with propylthiouracil, gold thioglucose, and T4
indicated that the iodothyronine 5'-deiodinase in goat perirenal adipose
tissue is of the type I form; there was no evidence for the type II enzyme.
Affinity labeling of the iodothyronine 5'-deiodinase with bromoacetyl-rT3
or bromoacetyl-T4 was consistent with this view. In contrast to goats, only
the type II enzyme is evident in rats and mice. It is concluded that the
perirenal (brown) adipose tissue is likely to be a significant source of T3
for other tissues in newborn goats and that there are major species
variations in the form of iodothyronine 5'-deiodinase present in brown fat,
with the goat exclusively exhibiting type I.
