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On the Metabolism of Organic Acids by Clostridium Acetobutylicum Part VII 307 Muscle and Was Named Crotonase5)

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On the Metabolism of Organic Acids by Clostridium Acetobutylicum Part VII 307 Muscle and Was Named Crotonase5) [Agr. Biol. Chem., Vol.25, No.4, p.306～313, 1961] On the Metabolism of Organic Acids by Clostridium acetobutylicum Part VII. Reduction of Crotonic Acid By Hideo KATAGIRIand Tsunetake SUGIMORI Department of Agricultural Chemistry,Faculty of Agriculture, Kyoto University ReceivedSeptember 20, 1960 Molecular hydrogen was capable of generating the reduced coenzymes by the hydrogenase system of Clostridium acetobutylicum. It was pointed out that crotonic acid was activated and reduced quantitatively to butyric acid by intact cells and cell-free preparation of this organism in the presence of acetyl phosphate, 2, 3-dimercaptopropanol (BAL) and hydrogen gas. INTRODUCTION tyric acid would involve one step of dehydra- In the fermentation of hexoses by acetone- tion and one step of reduction as described butanol fermentation bacteria, it is well below. known that pyruvic acid, which is derived or from hexose-diphosphate through the action of metalloaldolase1), is cleaved to acetyl-CoA and carbon dioxide2,3). It is with no doubt that two molecules of acetyl-CoA are con- Two types of unsaturated acids, namely both densed in forming acetoacetyl-CoA, and that vinylacetic and crotonic acids, are proposed as the latter is a common precursor of both the dehydrated intermediates. According to acetone and butyl compounds such as butyric the investigations on fatty acids metabolism acid and butyl alcohol. These butyl com- in animals, so-called Knoop's β-oxidation pounds are formed from acetoacetyl-CoA mechanism is shown as follows. through several steps of reduction. Gavard and Descourtieux4) found that the reduction R-CH2-CH2-CH2-CO-SCoA →R-CH2-CH=CH-CO-SCoA of acetoacetyl-CoA to β-hydroxybutyryl-CoA →R-CH2-CHOH-CH2-CO-SCoA was coupled with the dehydrogenation of →R-CH2-CO-CH2-CO-SCoA triose-phosphate in Embden-Meyerhof-Parnas →R-CH2-CO-SCoA+CH3-CO-SCoA→etc. pathway. In regard to the pathway from β- In this scheme -COSCoA means an acyl-CoA hydroxybutyryl-CoA to butyric acid, however, derivative. It was pointed out that each there has been no clear explanation with reaction in this scheme was reversible. These Clostridium acetobutylicum. As a matter of facts suggest that the pathway from β-hydroxy- course, it is expected that the pathway from butyryl-CoA to butyryl-CoA or butyric acid β-hydroxybutyryl-CoA to butyryl-CoA or bu- in Cl. acetobutylicum might be analogous to 1) R. Gavard, Compt. rend., 238, 1620 (1954). the reversal of β-oxidation. The enzyme 2) R. S. Wolfe and D. J. O'Kane, J. Biol. Chem., 205, 755 (1953) . which catalyzes dehydration of β-hydroxy- 3) E. R. Stadtman, J. Biol. Chem., 196, 535 (1952). 4) R. Gavard and H. Descourtieux, Compt. rend., 239, 201 (1954). butyryl-CoA to crotonyl-CoA was isolated from On the Metabolism of Organic Acids by Clostridium acetobutylicum Part VII 307 muscle and was named crotonase5). But an MATERIALS AND METHODS enzyme corresponding to crotonase has not Enzyme Preparations been found in Clostridium bacteria. It is Cl. acetobutylicum grown in Speakman's culture presumable that the reduction reaction from medium was collected by centrifugation. After wash- butenoyl-compound to butyric acid would be ing with distilled water, the wet cells were suspended somehow coupled with dehydrogenation of in distilled water, 0.3 per cent sodium sulfide solution triose-phosphate or oxidative phosphoroclastic or 0.02M 2, 3-dimercaptopropanol (BAL) depending on the purpose of each experiment. reaction of pyruvate, because no other reac- For preparing dried cells, above mentioned cell-paste tion in which hydrogen atom is generated was spread as a film on the surface of a petri-dish and could be detected in this organism. From dried in vacuo on sulfuric acid. these points of view, the reduction of croto- Cell-free extract was prepared through sonic oscilla- nate by this organism was investigated. tion of forty ml of cell-suspension in 0.02M BAL It is well known that Clostridium bacteria containing about four grams of wet cells at 9KC for thirty minutes followed by centrifugation at 9,000rpm possess a hydrogenase system. Two types of hydrogenase are known in various bacteria6). for thirty minutes. One of them is found in Acetobacter, Azoto- Manometric Techniques for Hydrogen Uptake bacter and Hydrogenomonas, and is an irre- Warburg's manometers were used. Gas phase was exchanged by pure hydrogen, and the reaction was versible enzyme. This type of hydrogenase carried out at 30℃. activates molecular hydrogen in forming hydrogen atom. Another is the reversible Analysis of Volatile Acids Analysis of volatile acids such as crotonic and butyric one, which exists in Clostridium, Desulfo- acids was carried out by microdiffusion method and vibrio, anaerobic Micrococcus and Coli-aero- paper chromatography. Details of the methods were genes bacteria. The latter is not only capable similar to those described in Part VI8). of activating molecular hydrogen, but also Preparation of Acetyl-CoA Fraction liberating molecular hydrogen from reduced. According to the method by Peel and Barker9), coenzymes. It is with no doubt that the pro- acetyl phosphate and dried cells of Cl. acetobutylicum duction of hydrogen gas by Cl. acetobutylicum were treated as follows. Two ml of the reaction mix- is caused by this type of hydrogenase, since ture, which contained 10 micromoles of acetyl phos- the existence of hydrogenase in Cl. acetobutyli- phate, 100mg of dried cells, 0.5ml of 0.2M phosphate cum was demonstrated and its reversible func- buffer of pH 8.0 and 0.03 per cent sodium sulfide, was incubated at 30℃ for fifteen minutes. The mixture tion was also verified by Hongo7). In other was then adjusted to pH 3.5 by hydrochloric acid, and words, reduced coenzyme and molecular kept in boiling water bath for fifteen minutes. Un- hydrogen are mediated through reversible reacted acetyl phosphate is destroyed by this heat action of hydrogenase in this organism. It is treatment, but acetyl-CoA is not affected. After cool- expected, therefore, that molecular hydrogen ing, the mixture was neutralized by sodium hydroxide would be capable of generating the reduced and the solids were spun off. The clear supernatant coenzymes in the presence of active hydro- thus obtained was used as acetyl-CoA fraction. genase system. An attempt was made to show Miscellaneous Materials the utilization of gaseous hydrogen as the Crotonic acid, methylene blue, safranin T and BAL reducing agent in the reduction of crotonate were all of reagent grade. Hydrogen gas was generated to butyrate by this organism. through the reaction of zinc flour with dilute sulfuric acid and washed by acid, alkali, and water. Acetyl 5) J. R. Stern and A. del Campillo, J. Am. Chem. Soc., 75, 2277 phosphate was kindly supplied from Dr. I. Takeda. (1953). 6) H. Gest, Proc. Intern. Symp. Enz. Chem., 211 (1957). 8) H. Katagiri and T. Sugimori, This Journal, 25, 300 (1961). 7) M. Hongo, J. Agr. Chem. Soc. Japan, 32, 29 (1958). 9) J.L. Peel and H. A. Barker, Biochem. J., 62, 323 (1956). 308 Hideo KATAGIRI and Tsunetake SUGIMORI Methyl-viologen was provided by courtesy of Dr. K. TABLE I. REDUCTION OF DPN AND FAD BY Ito. CELL-FREE EXTRACT RESULTS AND DISCUSSION Activation of Molecular Hydrogen by Cell-suspension and Cell-free Extract Washed cells suspended in distilled water were capable of reducing methylene blue in vacuo in rather short period when the suspen- sion was newly prepared. This activity, how- ever, was rapidly depressed after storage for and incubated with sodium crotonate under several hours. Under atmospheric hydrogen, atmospheric hydrogen at pH 7.2 at 30℃. A these suspensions maintained such a reducing small amount of hydrogen was taken up. It activity for much longer periods. When sus- is presumable that the metabolic change of pended in 0.02M BAL, the reducing activity fatty acids would proceed in the intermediary for methylene blue was greatly stimulated and state of such acids, namely, energy-rich acyl maintained for about one week in ice-box. derivatives as compared with the mechanism Several dyestuffs having redox potentials lower found in animals as described previously. As than methylene blue, for instance safranin T acetyl-CoA is the precursor of butyl com- and methyl-viologen, were also readily reduced pounds formation of this organism, it is ex- by atmospheric hydrogen by cells of this organ- pected that intermediary energy-rich acyl ism suspended in BAL. These reduction was compounds might be acyl-CoA. It is proposed never detected when the cell-suspension was by Stadtman10) that CoA-linked reaction re- preheated at 100•Ž for ten minutes. It is quires reducing agents so as to make oxidized therefore evident that above mentioned reduc- CoA into active CoA-SH form. In this con- tion of several redox dyes is an enzymatic nection, several thiol compounds were ex- reaction. In other words, Cl. acetobutylicum amined. From the experiments on the effects is capable of activating molecular hydrogen of each 0.02 to 0.001M of several thiol com- and transporting activated hydrogen to pounds such as sodium sulfide, glutathione, methyl-viologen (E0=-0.446v), safranin T cysteine, thioglycollate and BAL, it was point- (E0=-0.289v) and methylene blue (E0= ed out that BAL was the most effective in +0.011v). stimulating the activity to take up hydrogen Employing a cell-free extract of the same with crotonate by cell-suspension. Table II organism, the enzymatic reduction of above shows the results obtained by use of dried described dyes was further verified under cells. atmospheric hydrogen. Moreover, it was con- It is evident from Table II that the hydro- firmed that the cell-free extract was able to gen uptake is enzymatic. The final molar reduce pyridine nucleotides and flavin nucleo- amount of volatile acids is equivalent to the tides readily with the aid of molecular hydro- initial within an experimental error.
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