Abstract
A five-component enzyme system which catalyzes synthesis of acetylphosphate from methyltetrahydrofolate (CH3THF) plus pyruvate has been purified from the homoacetate-fermenting bacterium, Clostridium thermoaceticum. One of the components was identified as the low potential electron carrier, ferredoxin, and the other 4 protein components have been designated F1, F2, F3, and F4. F1, F2, and F4 have been purified to homogeneity and, as estimated by gel filtration, have native molecular weights of 88,100, 58,900, and 255,000, respectively, while the subunit molecular weights obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis are 20,000, 25,500, and 120,000, respectively. F3 contains 3 to 4 protein bands and has not been characterized with respect to molecular weights. Acetylphosphate synthesis by the purified system is optimal at pH 6.0 and 65 degrees C and requires ATP, CoA, and, to a lesser extent, thiamin pyrophosphate and Fe2+. S-Adenosylmethionine is not required. The F1 component has been identified as phosphotransacetylase and in its absence, the product is acetyl-CoA. Some properties of the phosphotransacetylase are presented. A scheme is given indicating present views of the functions of the individual components.
Highlights
Afive-componentenzymesystemwhichcatalyzes synthesis of acetylphosphate from methyltetrahydrofolate (CH3THF)plus pyruvate has been purified from thehomoacetate-fermentingbacterium, Clostridium thermoaceticum
F1,Fz,Fa,and F4.F1,Fz, and F4have been purified to homogeneity and, as estimated by gel filtration, have native molecularweights of 88,100,58,900, and 255,000, respectively, while the subunit molecular weights obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis are20,000, 25,500, and 120,000, respectively
Work demonstrated that glucose was fermented via Embden-Meyerhof type cleavage [3,4],and thatCOzfiiation was somehow involved in the formation of the end product, acetate [5, 6]
Summary
CH3B12was shown to be a precursor of the methyl group of acetate [8, 33], and since C. thermoaceticum contains a numberof cobalamins which become methylated in l4COZpulse-labeling experiments [17],it was believed that a transmethylation between CH3-THF and a corrinoid enzyme might be an intermediate step in the conversion of pyruvate plus CH3THF to 2 acetate. This hypothesis was supported by a recent study in which a “corrinoid” enzyme was isolated which, together with crude extracts, facilitated this transmethylation from CHB-THF[18]. Cobalt nitrate contamed 0 . 5 8 nickell; sodxun, thlullycolate, 0.5. and flitrare of bviled tetrahydrofolate; CH3THF, methyltetrahydrofolate; Fd, ferredoxin; TPP, thiamin-pyrophosphate; SDS,sodium dodecyl sulfate; Mops, 3(N-morpho1ino)propanesulfonicacid; FAD, flavin adenine dinucleotide
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
