酢酸キナーゼ

関連する読書

酢酸キナーゼは酢酸産生過程における主要酵素であり、酢酸の最終産生を制御する。酢酸や乳酸などの有機酸は、代謝・増殖のための唯一の炭素源として利用される。酢酸代謝の最初の段階は酢酸の活性化であり、酢酸キナーゼ（AK）およびホスホトランスアセチラーゼ（PTA）による触媒を要する。すなわち、ATPの関与下でAKにより酢酸がリン酸化されアセチルリン酸となり、続いてアセチルリン酸はPTAの触媒によりアセチルCoAへ変換され、クエン酸回路（TCA回路）に入り酢酸代謝が進行する。

図1．酢酸キナーゼのタンパク質構造。

概要

酢酸キナーゼは、ASKHA（Acetate and Sugar Kinases, Hsp70, Actin）ホスホトランスフェラーゼ・スーパーファミリーに属する。多様な生物に広く存在し、アセチルリン酸とADPから酢酸とATPを生成する可逆反応を触媒する。生体の炭素源代謝およびエネルギー代謝において重要な役割を担う。特に、嫌気または微好気環境（例：反芻動物のルーメン、深部岩盤）に生息する下等原核生物においては、本酵素はホスホトランスアセチラーゼとともに、生物による酢酸産生過程の鍵を構成する。同時に、本酵素は中間体であるアセチルリン酸を介して体内の他の生物学的反応を調節し得るため、当該生物において中枢的な役割を果たす。

研究および意義

参考文献

1. Grundy FJ.; ほか CcpAによるBacillus subtilis酢酸キナーゼ遺伝子の制御．J. Bacteriol. 1993, 175 (22): 7348–55.

1. Acetic acid is one of the end products of energy metabolism of most facultative and strictly anaerobic microorganisms. Conversely, acetic acid also has the effect of regulating central metabolism and hydrogen production metabolism. During the operation of the biological hydrogen production reactor, the secretion of a large amount of acetic acid will cause the pH change in the reactor, and the pH change can change the type of fermentation of the microorganisms in the reactor, affect the stability of the reaction, and consequently inhibit the growth of bacteria. Growth reduces H₂ production; and the method of adjusting pH with alkali will increase production costs.
2. In the process of acetic acid production, acetate kinase is the key enzyme, which controls the final production of acetic acid. Therefore, clone the acetate kinase gene and study its physiological and biochemical effects in the metabolic pathway of hydrogen production, so as to provide a basis for optimizing the optimal hydrogen production metabolic process.
3. The enzyme activity regulation of PTA and AK in acetic acid metabolism is similar. Studies have also found that when wild Corynebacterium glutamicum grows on a medium that uses acetic acid (instead of glucose) as a carbon source, the enzyme activities of PTA and AK are significantly increased. This phenomenon is a concrete manifestation of the glucose effect in microbial carbon metabolism, which implies that these enzymes may have negative regulatory effects on the glucose substrate or positive regulatory effects on the acetic acid substrate in the link of gene expression.
4. In addition, when the amrGl gene is deleted or overexpressed, the regulation of PTA and AK enzyme activity has a certain change rule. According to the experimental results, the PTA and AK enzyme activities of the gene-deficient strains were significantly increased when they were grown on the glucose carbon source, and the basic medium containing the two carbon sources of glucose and acetic acid showed a single carbon source medium with acetate. The same enzyme activity. On the contrary, the overexpression strain of amrGl gene has a certain degree of reduction of PTA and AK enzyme activity on glucose medium.