Kleber H P
Institut für Biochemie, Fakultät für Biowissenschaften, Pharmazie und Psychologie, Universität Leipzig, Germany.
FEMS Microbiol Lett. 1997 Feb 1;147(1):1-9. doi: 10.1111/j.1574-6968.1997.tb10212.x.
L-(-)-Carnitine is a ubiquitously occurring substance, essential for the transport of long-chain fatty acids through the inner mitochondrial membrane. Bacteria are able to metabolize this trimethylammonium compound in three different ways. Some, especially Pseudomonas species, assimilate L-(-)-carnitine as sole source of carbon and nitrogen. The first catabolic step is catalysed by the L-(-)-carnitine dehydrogenase. Others, for instance, Acinetobacter species, degrade only the carbon backbone, with formation of trimethylamine. Finally, various members of the Enterobacteriaceae are able to convert carnitine, via crotonobetaine, to gamma-butyrobetaine in the presence of C and N sources and under anaerobic conditions. This two-step pathway, including a L-(-)-carnitine dehydratase and the crotonobetaine reductase, was demonstrated in Escherichia coli. The DNA sequence encompassing the cai genes of E. coli, which encode the carnitine pathway, has been determined. Some bacteria are also able to metabolize the non-physiological D-(+)-carnitine, which results as a waste product in some chemical procedures for L-(-)-carnitine production based on the resolution of racemic carnitine.
L-(-)-肉碱是一种普遍存在的物质，对于长链脂肪酸穿过线粒体内膜的转运至关重要。细菌能够通过三种不同方式代谢这种三甲铵化合物。一些细菌，尤其是假单胞菌属，将L-(-)-肉碱作为唯一的碳源和氮源进行同化。第一步分解代谢由L-(-)-肉碱脱氢酶催化。其他细菌，例如不动杆菌属，仅降解碳骨架，生成三甲胺。最后，肠杆菌科的各种成员能够在有碳源和氮源存在以及厌氧条件下，通过巴豆甜菜碱将肉碱转化为γ-丁酸甜菜碱。在大肠杆菌中证实了这条两步途径，包括L-(-)-肉碱脱水酶和巴豆甜菜碱还原酶。已经确定了大肠杆菌中包含编码肉碱途径的cai基因的DNA序列。一些细菌也能够代谢非生理性的D-(+)-肉碱，在某些基于外消旋肉碱拆分的L-(-)-肉碱生产化学过程中，D-(+)-肉碱是一种废品。
