West Thomas P
Department of Biology and Microbiology, South Dakota State University, Brookings, SD 57007, USA.
J Basic Microbiol. 2007 Oct;47(5):440-3. doi: 10.1002/jobm.200710333.
The regulation of pyrimidine formation in the opportunistic human pathogen Pseudomonas oryzihabitans was investigated at the level of enzyme synthesis and at the level of activity for the pyrimidine biosynthetic pathway enzyme aspartate transcarbamoylase. Although pyrimidine supplementation of succinate-grown P. oryzihabitans cells produced little effect on the de novo pyrimidine biosynthetic pathway enzyme activities, pyrimidine limitation experiments undertaken using an orotidine 5'-monophosphate decarboxylase mutant strain isolated from P. oryzihabitans ATCC 43272 indicated that repression of enzyme synthesis by pyrimidines was occurring. Following pyrimidine limitation of the succinate-grown decarboxylase mutant strain cells, aspartate transcarbamoylase and dihydroorotase activities were found to increase by about 3-fold while dihydroorotate dehydrogenase and orotate phosphoribosyltransferase activities were also observed to increase relative to their activities in the mutant strain cells grown on excess uracil. At the level of enzyme activity, aspartate transcarbamoylase in P. oryzihabitans was strongly inhibited by pyrophosphate, ADP, ATP and GTP in the presence of saturating substrate concentrations.
在机会性人类病原体栖稻假单胞菌中,对嘧啶生物合成途径中酶天冬氨酸转氨甲酰酶的合成水平和活性水平进行了嘧啶形成调控的研究。虽然向以琥珀酸盐为碳源培养的栖稻假单胞菌细胞补充嘧啶对从头嘧啶生物合成途径的酶活性影响很小,但使用从栖稻假单胞菌ATCC 43272分离得到的乳清苷5'-单磷酸脱羧酶突变株进行的嘧啶限制实验表明,嘧啶正在对酶的合成产生阻遏作用。在以琥珀酸盐为碳源培养的脱羧酶突变株细胞受到嘧啶限制后,发现天冬氨酸转氨甲酰酶和二氢乳清酸酶的活性增加了约3倍,同时相对于在过量尿嘧啶上生长的突变株细胞,二氢乳清酸脱氢酶和乳清酸磷酸核糖基转移酶的活性也有所增加。在酶活性水平上,在底物浓度饱和的情况下,栖稻假单胞菌中的天冬氨酸转氨甲酰酶受到焦磷酸、ADP、ATP和GTP的强烈抑制。