Cystathionine γ-synthase from Arabidopsis thaliana:: purification and biochemical characterization of the recombinant enzyme overexpressed in Escherichia coli

被引:70
作者
Ravanel, S [1 ]
Gakière, B [1 ]
Job, D [1 ]
Douce, R [1 ]
机构
[1] Rhone Poulenc Agrochim, Lab Mixte, CNRS, UMR41, F-69263 Lyon 09, France
关键词
D O I
10.1042/bj3310639
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Cystathionine gamma-synthase catalyses the first reaction specific for methionine biosynthesis in plants, the gamma-replacement of the phosphoryl substituent of O-phosphohomoserine by cysteine, A cDNA encoding cystathionine gamma-synthase from Arabidopsis thaliana has been cloned and used to overexpress the enzyme in Escherichia coli. The native recombinant enzyme is a homotetramer composed of 53 kDa subunits, each being tightly associated with one molecule of pyridoxal 5'-phosphate that binds at lysine-379 of the protein precursor. The replacement reaction follows a Ping Pong mechanism with a V-max of 33.6 units/mg and K-m values of 2.5 mM and 460 mu M for O-phosphohomoserine and cysteine respectively. The protective effect of O-phosphohomoserine against enzyme inactivation by propargylglycine indicated that the K-d for the substrate is approx. 1/2500 of its K-d value. Thus most of these biochemical properties are similar to those previously reported for plant and bacterial cystathionine gamma-synthases. However, the plant enzyme differs markedly from its enterobacterial counterparts because it catalyses a very faint gamma-elimination of O-phosphohomoserine in the absence of cysteine, this process being about 1/2700 as fast as the gamma-replacement reaction and approx. 1/1500 as fast as the gamma-elimination catalysed by the E. coli enzyme. This huge difference could be attributed to the inability of the A. thaliana cystathionine gamma-synthase to accumulate a long-wavelength-absorbing species that is characteristic for the efficient gamma-elimination reaction catalysed by the enterobacterial enzyme.
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页码:639 / 648
页数:10
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