ASPECTS RELATED TO MEVALONATE BIOSYNTHESIS IN PLANTS

被引:55
作者
BACH, TJ [1 ]
BORONAT, A [1 ]
CAELLES, C [1 ]
FERRER, A [1 ]
WEBER, T [1 ]
WETTSTEIN, A [1 ]
机构
[1] UNIV BARCELONA, FAC FARM, UNITAT BIOQUIM, E-08028 BARCELONA, SPAIN
关键词
D O I
10.1007/BF02536429
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
We purified and characterized a membrane-associated enzyme system from radish (Raphanus sativus L.) that is capable of converting acetyl-CoA into 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA). The enzyme system apparently comprises acetoacetyl-CoA thiolase (EC 2.3.1.9) and HMG-CoA synthase (EC 4.1.3.5). Its activity in vitro can be strongly stimulated by Fe(II). When ferrous ions are applied chelated with ethylenediaminetetraacetate, citrate or adenosine 5-triphosphate (ATP), the stimulation is further increased. Stimulation is due to a higher catalytic efficiency as indicated by an increase in V(max), whereas the affinity of the enzyme towards acetyl-CoA remains constant (K(m) = 6-mu-M). A considerable portion of HMG-CoA lyase activity is associated with the same membranes. HMG-CoA lyase (EC 4.1.3.4) is also solubilized and partially co-purified. Its activity requires comparatively high concentrations of Mg2+. The conversion of HMG-CoA to mevalonic acid is catalyzed by HMG-CoA reductase (EC 1.1.1.34) that is associated with the same membranes. By cDNA encoding the Arabidopsis HMG-CoA reductase, we isolated a corresponding gene from a cDNA library newly established from etiolated radish seedlings. This full-length cDNA, referred to as lambda-cRS3, encodes a polypeptide of 583 amino acids with a molecular mass of about 63 kDa. The hydropathy profile suggests the presence of two hydrophobic membrane-spanning domains within the N-terminal 165 amino acids. The carboxy-terminal part, where the catalytic site resides, is highly conserved in all eukaryotic HMG-CoA reductase genes sequenced so far.
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页码:637 / 648
页数:12
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