Falcon (Edison Scientific) deep research report: rat Gstt1 (UniProt Q01579), glutathione S-transferase theta-1
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Falcon confirms gene identity - rat Gstt1/GSTT1-1 is the historical theta-class cytosolic GST 5-5, purified as a homodimer from rat liver cytosol, distinct from the related theta enzyme GSTT2-2.
"Rat **Gstt1/GSTT1-1** corresponds to the historical rat **GST 5-5** enzyme: a **theta-class, soluble cytosolic glutathione S-transferase** purified from rat liver cytosol as a homodimer with an apparent subunit size of about **28 kDa**"
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Falcon corroborates the canonical glutathione transferase reaction (EC 2.5.1.18) as the core function of rat GSTT1-1.
"Its core reaction is the canonical GST reaction (**EC 2.5.1.18**): **glutathione conjugation of electrophilic substrates**; theta-class GSTT1-1 is especially notable because some conjugation reactions contribute to **bioactivation**, not just detoxification"
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Falcon corroborates rat GSTT1-1 dichloromethane (DCM) transferase activity with direct rat biochemical specific-activity measurements, supporting the dichloromethane metabolic process and alkylhalidase annotations.
"In rat biochemical assays, GSTT1-1 shows substantial activity toward **dichloromethane (DCM)** and model substrates including **EPNP** and **4-nitrobenzyl chloride**, with reported specific activities of **7.8, 35.2, and 7.8 mmol/min/mg**, respectively; it also has **glutathione peroxidase activity** toward **cumene hydroperoxide** (**24.7 mmol/min/mg**)"
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Falcon directly supports rat GSTT1-1 glutathione peroxidase activity toward cumene hydroperoxide.
"In addition, GSTT1-1 showed strong **glutathione peroxidase activity** (a glutathione-dependent reduction) toward **cumene hydroperoxide** (**24.7 mmol/min/mg**), and the study reports that theta-class GSTs have **low activity toward CDNB** compared with many other cytosolic GSTs."
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Falcon corroborates cytosolic localization - rat GSTT1-1 was purified from rat liver cytosol as a soluble (not microsomal/mitochondrial) enzyme.
"A primary biochemical characterization purified **rat liver theta-class GSTT1-1** from **rat liver cytosol**, establishing it as a soluble enzyme (not microsomal/mitochondrial in this preparation)."
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Falcon explains that DCM/dihaloalkane DNA damage and mutagenicity is a downstream consequence of GST-catalyzed bioactivation to reactive intermediates, not the direct enzyme reaction - supporting the over-annotation call on DNA modification and xenobiotic-response context terms.
"A review summarizing theta-class function states that rat GSTT1-1 (form 5-5) conjugates **ethylene dibromide**, generating an electrophilic intermediate capable of forming adducts, and also describes **Ames-test–detectable mutagenicity** when rat GSTT1-1 is expressed in bacteria and incubated with dihaloalkanes."
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CAVEAT (paralog): Falcon notes substrate-preference differences between GSTT1-1 and the distinct rat theta enzyme GSTT2-2 (e.g., GSTT2-2 prefers fatty-acid hydroperoxides) - GSTT2-2-specific substrate claims must not be imported onto Gstt1.
"GSTT1-1 preferred cumene hydroperoxide; GSTT2-2 preferred fatty-acid hydroperoxides; theta-class GSTs together ~0.5% of total cytosolic protein"