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A granule-associated L-thyroxine deiodinating system in the human leukocyte
Endocrinology
|March 1, 1976
Summary
Human leukocytes, specifically their granule fraction, possess significant L-thyroxine (T4) deiodinase activity. This activity increases during phagocytosis, indicating a key role for leukocyte granules in thyroid hormone metabolism.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Leukocytes are known to deiodinate L-thyroxine (T4).
- This deiodination process is notably enhanced during phagocytosis.
Purpose of the Study:
- To pinpoint the subcellular location of T4 deiodination in human leukocytes.
- To characterize the nature of this deiodinative activity.
Main Methods:
- Human leukocytes (over 90% polymorphonuclear) were fractionated.
- Deiodinative activity of different cell fractions was assessed.
- Activity was measured before and after inducing phagocytosis with opsonized zymosan.
Main Results:
- The granule fraction exhibited the majority of T4 deiodinative activity.
- Phagocytosis induction significantly increased the T4 deiodinase activity in isolated granule fractions.
- The system demonstrated characteristics of an enzyme with a Km of approximately 10(-6)M.
Conclusions:
- T4 deiodinative activity in human leukocytes is primarily localized to the granule fraction.
- Leukocyte granule deiodinase activity is upregulated by phagocytosis.
- The identified system is likely an enzymatic process involved in thyroid hormone metabolism.
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