Enzymatic characterization of human mitochondrial C1-tetrahydrofolate synthase.

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Walkup AS, Appling DR

Enzymatic characterization of human mitochondrial C1-tetrahydrofolate synthase.

Arch Biochem Biophys. 2005 Oct 15;442(2):196-205. Epub 2005 Aug 30.

PubMed ID

16171773 [ View in PubMed

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Abstract

A human mitochondrial isozyme of C1-tetrahydrofolate (THF) synthase was previously identified by its similarity to the human cytoplasmic C1-THF synthase. All C1-THF synthases characterized to date, from yeast to human, are trifunctional, containing the activities of 5,10-methylene-THF dehydrogenase, 5,10-methenyl-THF cyclohydrolase, and 10-formyl-THF synthetase. Here we report on the enzymatic characterization of the recombinant human mitochondrial isozyme. Enzyme assays of purified human mitochondrial C1-THF synthase protein revealed only the presence of 10-formyl-THF synthetase activity. Gel filtration and crosslinking studies indicated that human mitochondrial C1-THF synthase exists as a homodimer in solution. Steady-state kinetic characterization of the 10-formyl-THF synthetase activity was performed using (6R,S)-H4-PteGlu1, (6R,S)-H4-PteGlu3, and (6R,S)-H4-PteGlu5 substrates. The (6R,S)-H4-PteGlun Km dropped from greater than 500 microM for the monoglutamate to 15 microM and 3.6 microM for the tri- and pentaglutamates, respectively. The Km values for formate and ATP also are lowered when THF polyglutamates are used. The formate Km dropped 79-fold and the ATP Km dropped more than 5-fold when (6R,S)-H4-PteGlu5 was used as the substrate in place of (6R,S)-H4-PteGlu1.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Tetrahydrofolic acid	C-1-tetrahydrofolate synthase, cytoplasmic	Protein	Humans	Unknown	Cofactor	Details