Sánchez J C, Gímenez R, Schneider A, Fessner W D, Baldomà L, Aguilar J, Badía J
Department of Biochemistry, School of Pharmacy, University of Barcelona, Spain.
J Biol Chem. 1994 Nov 25;269(47):29665-9.
A silent gene encoding a kinase that specifically phosphorylates L-xylulose was activated and rendered constitutive in mutant cells of Escherichia coli. L-Xylulose kinase was purified to homogeneity and found to be a dimer of two subunits of 55 kDa, highly specific for L-xylulose with a Km of 0.8 mM, a Vmax of 33 mumol/min/mg, and an optimum pH of 8.4. Physical (thin layer chromatography) and spectroscopic (nuclear magnetic resonance and optical rotation) characterization of the product of L-xylulose kinase indicated that the enzyme phosphorylated the sugar at position 5. The gene encoding L-xylulose kinase was mapped in the 80.2 min region of the chromosome by conjugation and transduction. Cloning and comparison of the restriction map with the Kohara map (Kohara, Y., Akiyame, K., and Isono, K. (1987) Cell 50, 495-501) located the gene between positions 3963 and 3965 kilobases. The molecular and functional features of L-xylulose kinase together with the location of the corresponding gene indicate that this enzyme did not derive from mutation of any other known kinase. The new kinase opens a route for the utilization of L-lyxose through the action of rhamnose permease, rhamnose isomerase, and the phosphorylation of the L-xylulose formed to L-xylulose 5-phosphate, which is then introduced into the pentose phosphate pathway for subsequent metabolism.
一个编码特异性磷酸化L-木酮糖的激酶的沉默基因在大肠杆菌突变细胞中被激活并呈现组成型表达。L-木酮糖激酶被纯化至同质，发现它是由两个55 kDa亚基组成的二聚体，对L-木酮糖具有高度特异性，Km为0.8 mM，Vmax为33 μmol/min/mg，最适pH为8.4。L-木酮糖激酶产物的物理（薄层色谱）和光谱（核磁共振和旋光）表征表明该酶在第5位磷酸化该糖。通过接合和转导将编码L-木酮糖激酶的基因定位在染色体的80.2分钟区域。克隆该基因并将其限制性图谱与小原图谱（小原洋、秋山和夫、矶野克，（1987年）《细胞》50卷，495 - 501页）进行比较，将该基因定位在3963至3965千碱基之间。L-木酮糖激酶的分子和功能特征以及相应基因的位置表明该酶并非源自任何其他已知激酶的突变。这种新的激酶通过鼠李糖通透酶、鼠李糖异构酶的作用以及将形成的L-木酮糖磷酸化为L-木酮糖5-磷酸，为利用L-来苏糖开辟了一条途径，然后L-木酮糖5-磷酸被引入戊糖磷酸途径进行后续代谢。
