紫云英根瘤菌109菌株吸氢的诱导表达——核苷、核苷酸与烟酸的促进效应

Expression of Hydrogenase System in Rhizobium astragalus Strain 109: Promotive Effects of Nucleotide and Nicotinic Acid

核苷酸和烟酸的添加,使紫云英根瘤菌109氢酶吸氢活性表达增加。cAMP(1 mmol/L),烟酸(70 mmol/L)的存在,缓解了葡萄糖酸钠或果糖引起的吸氢活性阻遏,cAMP的解阻遏效应在年轻的菌体(48 h)表现较为明显。但以MB为受体的破碎细胞吸氢活性则未见增加,烟酸的促进效应受到氯霉素(40μg/ml)的抑制。其他核苷或核苷酸,如腺嘌呤,尿嘧啶,ATP,ADP,AMP,UMP,UTP都能促进吸氢活性的表达。诱导氢酶前,细胞ATP库已处于低水平,并保持稳定,添加琥珀酸盐后,ATP库水平提高,吸氢活性表达受抑。

A promotive effect of nucleotides and nicotinic acid on the H_2-uptake (Hup) activity was observed in Rhizobium astragalus strain 109. The Hup activity was increased, and the repression by fructose and gluconate of the Hup activity was alleviated by cAMP (1 mmol/L). The significant derepression of cAMP occurred when bacteria were young. AMP, ADP, ATP, UTP, UMP, Ade or URA could increase the Hup activity. In the cell-free extracts of the cultures with cAMP, the increase in Hup activity was not observed using MB as electron acceptor. Nicotinic acid increased the Hup activity and alleviated the repression by fructose. The promotive effects were blocked by chloramphenicol (40 μg/ml). Assaying of intraeellular ATP pool showed that the ATP content was at low level prior to enzyme induction. The level was increased by adding succinate (20 mmol/L) and the Hup activity was expressed. It was suggested that the expression of Hup activity was regulated by the level of energy charge which may be changed by the metabolism of nucleotides.