In:
Applied and Environmental Microbiology, American Society for Microbiology, Vol. 70, No. 3 ( 2004-03), p. 1397-1404
Abstract:
The araA gene encoding l -arabinose isomerase (AI) from the hyperthermophilic bacterium Thermotoga maritima was cloned and overexpressed in Escherichia coli as a fusion protein containing a C-terminal hexahistidine sequence. This gene encodes a 497-amino-acid protein with a calculated molecular weight of 56,658. The recombinant enzyme was purified to homogeneity by heat precipitation followed by Ni 2+ affinity chromatography. The native enzyme was estimated by gel filtration chromatography to be a homotetramer with a molecular mass of 232 kDa. The purified recombinant enzyme had an isoelectric point of 5.7 and exhibited maximal activity at 90°C and pH 7.5 under the assay conditions used. Its apparent K m values for l -arabinose and d -galactose were 31 and 60 mM, respectively; the apparent V max values (at 90°C) were 41.3 U/mg ( l -arabinose) and 8.9 U/mg ( d -galactose), and the catalytic efficiencies ( k cat / K m ) of the enzyme were 74.8 mM −1 · min −1 ( l -arabinose) and 8.5 mM −1 · min −1 ( d -galactose). Although the T. maritima AI exhibited high levels of amino acid sequence similarity ( 〉 70%) to other heat-labile mesophilic AIs, it had greater thermostability and higher catalytic efficiency than its mesophilic counterparts at elevated temperatures. In addition, it was more thermostable in the presence of Mn 2+ and/or Co 2+ than in the absence of these ions. The enzyme carried out the isomerization of d -galactose to d -tagatose with a conversion yield of 56% for 6 h at 80°C.
Type of Medium:
Online Resource
ISSN:
0099-2240
,
1098-5336
DOI:
10.1128/AEM.70.3.1397-1404.2004
Language:
English
Publisher:
American Society for Microbiology
Publication Date:
2004
detail.hit.zdb_id:
223011-2
detail.hit.zdb_id:
1478346-0
SSG:
12
Permalink