Literature summary for 1.8.3.1 extracted from

Davis, A.C.; Johnson-Winters, K.; Arnold, A.R.; Tollin, G.; Enemark, J.H.
Kinetic results for mutations of conserved residues H304 and R309 of human sulfite oxidase point to mechanistic complexities (2014), Metallomics, 6, 1664-1670 .

Search for more literature for 1.8.3.1

Cloned(Commentary)

Cloned (Comment)	Organism
recombinant expression of wild-type and mutant enzymes	Homo sapiens

Protein Variants

Protein Variants	Comment	Organism
H304A R309H	site-directed mutagenesis, a mutation that removes the charge, hydrogen bonding, and is of smaller size, shows a decrease in Ksulfite m , thus binding sulfite more efficiently than the wild-type, kcat is increased compared to wild-type	Homo sapiens
H304R/R309H	site-directed mutagenesis, the mutant shows altered kinetics and reaction rates compared to the wild-type enzyme	Homo sapiens
K322R	site-directed mutagenesis, the mutant shows altered kinetics and reaction rates compared to the wild-type enzyme	Homo sapiens
additional information	all of the mutants show decreased rates of intramolecular electron transfer (IET) but increased steady-state rates of catalysis, IET is not the rate determining step for any of the mutations. Redox potentials of wild-tyype and mutant enzymes, overview	Homo sapiens
R160Q	site-directed mutagenesis, inactive mutant	Homo sapiens
R309E	site-directed mutagenesis, the mutant shows altered kinetics and reaction rates compared to the wild-type enzyme, mutant R309E, which shows the greatest increase in activity, also shows the greatest increase in Km	Homo sapiens
R309H	site-directed mutagenesis, the mutant shows altered kinetics and reaction rates compared to the wild-type enzyme, purified R309H mutant enzyme has substantially increased catalytic activity and a slightly less efficient Km sulfite compared to the wild-type enzyme	Homo sapiens

KM Value [mM]

KM Value [mM]	KM Value Maximum [mM]	Substrate	Comment	Organism	Structure
additional information	-	additional information	Michaelis-Menten steady-state kinetics of wild-type and mutant enzymes. All of the mutants show decreased rates of intramolecular electron transfer (IET) but increased steady-state rates of catalysis	Homo sapiens

Metals/Ions

Metals/Ions	Comment	Organism	Structure
Fe3+	-	Homo sapiens
Mo6+	-	Homo sapiens

Natural Substrates/ Products (Substrates)

Natural Substrates	Organism	Comment (Nat. Sub.)	Natural Products	Comment (Nat. Pro.)	Rev.	Reac.
sulfite + O2 + H2O	Homo sapiens	-	sulfate + H2O2	-	?

Organism

Organism	UniProt	Comment	Textmining
Homo sapiens	P51687	-	-

Purification (Commentary)

Purification (Comment)	Organism
recombinant wild-type and mutant enzymes	Homo sapiens

Reaction

Reaction	Comment	Organism	Reaction ID
sulfite + O2 + H2O = sulfate + H2O2	catalytic cycle and electron transfer steps, and proposed oxidation state changes occurring at the Mo and Fe centers of one subunit of human sulfite oxidase during the catalytic oxidation of sulfite and the concomitant reduction of (cyt c)ox, overview	Homo sapiens	a

Substrates and Products (Substrate)

Substrates	Comment Substrates	Organism	Products	Comment (Products)	Rev.	Reac.
additional information	regeneration of the enzyme includes two, one-electron intramolecular electron transfers (IET) from the molybdenum (Mo) to the heme Fe and two, one-electron intermolecular electron transfers from the Fe to external ferricytochrome c	Homo sapiens	?	-	?
sulfite + O2 + H2O	-	Homo sapiens	sulfate + H2O2	-	?

Temperature Optimum [°C]

Temperature Optimum [°C]	Temperature Optimum Maximum [°C]	Comment	Organism
25	-	assay at	Homo sapiens

pH Optimum

pH Optimum Minimum	pH Optimum Maximum	Comment	Organism
6.8	7.6	assay at	Homo sapiens

Cofactor

Cofactor	Comment	Organism	Structure
cytochrome c	-	Homo sapiens
heme	-	Homo sapiens
molybdenum cofactor	three conserved residues (H304, R309, K322) are hydrogen bonded to the phosphate group of the molybdenum cofactor	Homo sapiens

General Information

General Information	Comment	Organism
malfunction	R309H and K322R mutations are responsible for isolated sulfite oxidase deficiency	Homo sapiens

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Release 2023.1 (January 2023)