Species differences in liver type I iodothyronine deiodinase.
The type I iodothyronine deiodinase (ID-I) of liver is an important enzyme for the conversion of the prohormone thyroxine (T4) to the active thyroid hormone 3,3',5-triiodothyronine (T3). Because it is an integral membrane protein of low abundance, purification of ID-I from rat liver has proven to be difficult. We have analyzed ID-I in liver microsomal fractions from various animals to reveal possible species differences and to explore alternative sources for the isolation of the enzyme. ID-I was characterized by enzyme assay with 3,3',5'-triiodothyronine (rT3) as the preferred substrate and by affinity-labeling with N-bromoacetyl-[125I]T3 (BrAc[125I]T3). Labeled ID-I subunit was identified and quantified by SDS-PAGE and autoradiography. The Mr of ID-I in the species investigated varied between 25.7 and 29.1 kDa. Rat and dog liver microsomes had a markedly higher enzyme content than microsomes of human, mouse, rabbit, cow, pig, sheep, goat, chicken or duck liver. Rat liver microsomes showed the highest ID-I activity of all species examined. Turnover numbers for ID-I varied between 264 and 1059 min-1, with rabbit and goat showing the highest values. However, dog liver ID-I displayed an exceptionally low turnover number of 78 min-1. In conclusion, ID-I has similar properties in all species examined with the notable exception of dog.
Schoenmakers
C H
CH
Department of Internal Medicine III, Erasmus University Medical School, Rotterdam, Netherlands.
Pigmans
I G
IG
Visser
T J
TJ
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007453:Iodide Peroxidase / Q000302:isolation & purification / Q000378:metabolism*; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008862:Microsomes, Liver / Q000201:enzymology*; D008970:Molecular Weight; D013045:Species Specificity; D013379:Substrate Specificity; D014284:Triiodothyronine / Q000031:analogs & derivatives / Q000378:metabolism
D007527:Isoenzymes; D046911:Macromolecular Substances; D014284:Triiodothyronine; C036219:N-bromoacetyl-3,3',5-triiodothyronine; D007453:Iodide Peroxidase