Disease relevance of SOX

• When overexpressed in Escherichia coli, AtSOX enhanced growth on sarcosine as sole nitrogen source, showing that it has SOX activity in vivo, and the recombinant protein catalyzed the oxidation of sarcosine to glycine, formaldehyde, and H(2) O(2) in vitro [1].
• Identification and characterization of a novel bacterial sulfite oxidase with no heme binding domain from Deinococcus radiodurans [2].
• A novel sulfite oxidase has been identified from Thermus thermophilus AT62 [3].

High impact information on SOX

• These data indicate that pipecolate is the endogenous substrate for SOX in plants and that plants can utilize exogenous sarcosine opportunistically, sarcosine being a common soil metabolite [1].
• Consistent with a low level of AtSOX expression, Arabidopsis plantlets slowly metabolized supplied [(14)C]sarcosine to glycine and serine [1].
• Although AtSOX lacks a typical peroxisome-targeting signal, in vitro assays established that it is imported into peroxisomes [1].
• Gas chromatography-mass spectrometry analysis revealed low levels of pipecolate but almost no sarcosine in wild type Arabidopsis and showed that pipecolate but not sarcosine accumulated 6-fold when AtSOX expression was suppressed by RNA interference [1].
• Its presence in plants was unsuspected until the Arabidopsis genome was found to encode a protein (AtSOX) with approximately 33% sequence identity to mammalian and bacterial SOXs [1].

Biological context of SOX

• In contrast to homologous animal enzymes, At-SO lacks the heme domain, which is evident both from the amino acid sequence and from its enzymological and spectral properties [4].
• It is proposed that, depending on the conformation of Arg374, the active site of At-SO may be in "closed" or "open" forms that differ in the degree of accessibility of the Mo center to substrate and water molecules [5].

Anatomical context of SOX

• Sulfite oxidase from T. thermophilus, purified to homogeneity, is a monomeric enzyme with an apparent molecular mass of 39.1 kDa and is almost exclusively located in the periplasm fraction [3].

Associations of SOX with chemical compounds

• In mammals and birds, sulfite oxidase (SO) is a homodimeric molybdenum enzyme consisting of an N-terminal heme domain and a C-terminal molybdenum domain (EC ) [4].
• Reduction of At-SO with sulfite at high pH generates the well-known high-pH (hpH) signal common to all sulfite oxidizing enzymes [5].
• It is suggested that at low pH the sulfite-reduced At-SO has coordinated sulfate and is in the "closed form". Reoxidation to Mo(V) by ferricyanide leaves bound sulfate trapped at the active site, and consequently, there are no ligands with exchangeable protons [5].
• On the other hand, reduction of At-SO with Ti(III) citrate at pH 6 generates a Mo(V) signal with large hyperfine splittings from a single exchangeable proton, as is typically observed for lpH SO from vertebrates [5].
• The Arabidopsis AtMCP and rice OsMCP genes which encode proteins highly homologous to molybdoenzymes of the sulphite oxidase family were isolated and characterized [6].

References