Source:http://biocyc.org/biopax/biopax-level3Catalysis169761
| Predicate | Object |
|---|---|
| rdf:type | |
| biopax3:controlType |
ACTIVATION
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| biopax3:controlled | |
| biopax3:comment |
This enzyme catalyzes the ω-hydroxylation of the side chain of |FRAME: ALPHA-TOCOPHEROL|. This is the first step in the catabolism of tocopherols and tocotrienols. Its activity using |FRAME: ALPHA-TOCOPHEROL| as substrate was demonstrated using cultures of HepG2 cells, human liver microsomal preparations, and insect cell microsomes selectively expressing the recombinant human liver enzyme |CITS: [17284776]|. The use of |FRAME: ALPHA-TOCOPHEROL|, or racemic α-tocopherol as substrate showed Michaelis-Menten kinetics. However, other tocopherols and tocol showed both Michaelis Menten and Hill kinetics. Tocotrienols showed only Hill kinetics, indicating positive cooperativity. Substrate structural features influencing the kinetics included the position of methyl groups on the chromanol ring and the presence of double bonds in the side chain |CITS: [17284776]|. Although other tocopherols, such as |FRAME: GAMA-TOCOPHEROL|, showed lower <i>K</i><sub>m</sub> values than |FRAME: ALPHA-TOCOPHEROL|, the higher activity of |FRAME: ALPHA-TOCOPHEROL| <i>in vivo</i> is due to its superior retention in the body. Differential rates of catabolism of tocopherols and tocotrienols, as well as selective retention of |FRAME: ALPHA-TOCOPHEROL| via the hepatic α-tocopherol transfer protein appear to be responsible (in |CITS: [17284776]|). The <i>K</i><sub>m</sub> for |FRAME: ALPHA-TOCOPHEROL| shown here is for the recombinant human enzyme selectively expressed in insect cell microsomes |CITS: [17284776]|.
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| biopax3:xref | |
| biopax3:controller | |
| biopax3:dataSource | |
| biopax3:displayName |
α-tocopherol ω-hydroxylase
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| biopax3:name |
tocopherol ω-hydroxylase
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| biopax3:evidence | |
| biopax3:standardName |
α-tocopherol ω-hydroxylase
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