Cánovas Manuel, Torroglosa Tomás, Kleber Hans-Peter, Iborra Jose Luis
Department of Biochemistry and Molecular Biology B and Immunology, Faculty of Chemistry, University of Murcia, 30100 Murcia, Spain.
J Basic Microbiol. 2003;43(4):259-68. doi: 10.1002/jobm.200390029.
The biotransformation of crotonobetaine and D(+)-carnitine into L(-)-carnitine is affected by salt stress in the resting cells of E. coli O44 K74 and the transformed E. coli K38 pT7-5KE32. A yield of 65 and 80% of L(-)-carnitine, respectively, were obtained with 0.5 M NaCl with the wild and transformed strain compared with the 40% obtained with the control. Higher salt levels reduced the conversion. In L(-)-carnitine transport studies using both strains, the transformed strain presented slightly lower apparent K(m) and V values. Arsenate reduced both the transport and biotransformation of crotono-betaine in the presence or absence of 0.5 M NaCl, whereas vanadate only inhibited these processes under salt stress conditions. Hg(II) inhibited both the transport and biotransformation and Pb(II) reduced the biotransformation only under salt stress conditions. Cu(II) produced a significantly higher decrease than Pb(II) in the biotransformation with both substrates in the absence of salt stress conditions, but only affected transport in the presence of such conditions. Furthermore, salt stress affected the CaiT transporter for L(-)-carnitine and crotonobetaine and induced ProU and ProP in the absence of the inducer of the L(-)-carnitine metabolism. It is highly likely that the increase in L(-)-carnitine production was not only due to improved transport but also to the permeabilization effect caused by NaCl, as transport and 1-N-phenylnaphthylamine uptake studies revealed.
在大肠杆菌O44 K74及转化后的大肠杆菌K38 pT7 - 5KE32的静息细胞中，巴豆甜菜碱和D(+)-肉碱向L(-)-肉碱的生物转化受盐胁迫影响。与对照获得的40%相比，在0.5 M NaCl条件下，野生型和转化菌株分别获得了65%和80%的L(-)-肉碱产量。更高的盐浓度降低了转化率。在使用这两种菌株进行的L(-)-肉碱转运研究中，转化菌株的表观K(m)和V值略低。在存在或不存在0.5 M NaCl的情况下，砷酸盐均降低了巴豆甜菜碱的转运和生物转化，而钒酸盐仅在盐胁迫条件下抑制这些过程。Hg(II)抑制了转运和生物转化，而Pb(II)仅在盐胁迫条件下降低生物转化。在无盐胁迫条件下，Cu(II)对两种底物生物转化的降低作用均显著高于Pb(II)，但仅在存在盐胁迫条件时影响转运。此外，盐胁迫影响了L(-)-肉碱和巴豆甜菜碱的CaiT转运体，并在缺乏L(-)-肉碱代谢诱导剂的情况下诱导了ProU和ProP。正如转运和1 - N - 苯基萘胺摄取研究所揭示的，L(-)-肉碱产量的增加很可能不仅归因于转运的改善，还归因于NaCl引起的通透化效应。
