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Methanogenesis, Fatty Acid Synthesis, and Cobamide Coenzymes: the Work of Horace A. Barker

2005; Elsevier BV; Volume: 280; Issue: 33 Linguagem: Inglês

10.1016/s0021-9258(20)56434-x

1083-351X

Nicole Kresge, Robert Simoni, Robert L. Hill,

Genomics and Phylogenetic Studies

The Enzymatic Synthesis of Cobamide Coenzymes (Brady, R. O., Castanera, E. G., and Barker, H. A. (1962) J. Biol. Chem. 237, 2325–2332) Horace Albert Barker (1907–2000) was educated at Stanford University and earned a Ph.D. in chemistry in 1933. He then spent the next 2 years with Dutch microbiologist C. B. van Niel at the Hopkins Marine Station isolating marine diatoms and dinoflagellates and studying their physiology and metabolism. Barker also absorbed the concepts of the “Delft school” of microbiology, namely that microorganisms can best be understood and classified by their chemical activities. This time spent at Hopkins Marine Station combined with Van Niel's enthusiasm and gifted teaching and research skills persuaded Barker to choose microbiology for his own career. In 1935 Barker went to the Netherlands to study with van Niel's mentor, A. J. Kluyver, in the Delft Microbiology Laboratory. There he initiated studies on three topics that he would pursue throughout his career: the biochemistry of methanogenesis, the production of fatty acids by microbial fermentation, and the anaerobic degradation of glutamate. Barker returned to California in 1936 to take a position as a soil microbiologist in the Agricultural Experiment Station at the University of California, Berkeley. He remained at Berkeley for his entire career, holding appointments first in plant nutrition, then plant and microbial biochemistry, and finally in the new Department of Biochemistry. Because of the proximity of the Berkeley Radiation Laboratory, radioactive carbon isotopes became available to Berkeley researchers early on. In collaboration with Sam Ruben, Zev Hassid, and Martin Kamen, Barker began investigating methanogenesis in the fermentations of methanol and acetate using 11CO2. They were able to show that 11CO2 was converted to radioactive methane, even though the half-life of 11C was only 20 min. When the longer lived 14C became available, Barker and his colleagues were able to work out the details of methane biosynthesis and showed that during acetate fermentation methane was derived from the methyl group of acetate and the carboxyl group was converted to carbon dioxide. In 1956 Barker published a generalized pathway for the formation of methane from acetate, methanol, or carbon dioxide (1Barker H.A. Ind. Eng. Chem. 1956; 48: 1438-1442Crossref Scopus (15) Google Scholar). In the early 1940s Barker became involved in a department of food technology wartime project in which he investigated the deterioration of dried fruit during storage. After the War, Barker started studying fatty acid synthesis in Clostridium kluyveri with Earl R. Stadtman. The details of these investigations were published in a previous Journal of Biological Chemistry (JBC) Classic (2Stadtman E.R. Barker H.A. J. Biol. Chem. 1949; 180 (JBC Classics): 1085-1093Abstract Full Text PDF PubMed Google ScholarMura U. Chock P.B. Stadtman E.R. J. Biol. Chem. 1981; 256 (http://www.jbc.org/cgi/content/full/280/26/e23): 13022-13029Abstract Full Text PDF PubMed Google Scholar). Barker's research focus turned to glutamate degradation when Arthur Kornberg, who will be the subject of a future JBC Classic, isolated a histidine-degrading strain of C. tetanomorphum while visiting Barker's laboratory. Barker's student, Joseph Wachsman, investigated the early steps of histidine degradation and determined that glutamate is an intermediate in the degradation process. He then studied the degradation of glutamate by tracer and enzymatic methods and established that glutamate was degraded by a novel pathway. A clue to the nature of the pathway was provided when Wachsman identified mesaconic acid and 3-methyl-l-aspartate as intermediates in glutamate degradation. Chemical degradation of [14C]mesaconate formed from [4-14C]glutamate led to the conclusion that a novel isomerization of glutamate must occur during its conversion to mesaconate. A. Munch-Peterson determined that the isomerization was inhibited by charcoal treatment of the cell-free extracts and H. Weissbach and R. D. Smyth identified the charcoal-absorbable cofactor as a novel form of pseudovitamin B12. Barker and his co-workers soon isolated several forms of the new coenzyme. They also prepared an enzyme system from Propionibacterium shermanii that catalyzed the conversion of benzimidazolylhydroxocobamide and 5,6-dimethylbenzimidazolylcyanocobamide to their respective cobamide coenzymes. The JBC Classic reprinted here describes Barker's purification of the cobamide coenzyme-synthesizing enzyme from P. shermanii and presents the results of his studies on the chemical transformations involved in the biosynthesis of cobamide coenzymes. The experiments also confirmed previous observations that the adenosyl moiety of B12 coenzymes arises from the adenosine moiety of ATP. The impact of Barker's research earned him widespread recognition. In 1953 he was elected to the National Academy of Sciences. He received the 1965 Borden Award in Nutrition and the Hopkins Medal from the Biochemical Society. He was also named California Scientist of the Year in 1966 and was awarded the National Medal of Science in 1968 by President Lyndon Johnson. In 1988, the Biochemistry Building on the Berkeley campus was renamed H. A. Barker Hall. 1All biographical information on Horace A. Barker was taken from Refs. 3Switzer R.L. Stadtman E.R. Stadtman T.C. Biographical Memoir of H. A. Barker. 84. National Academy of Sciences, Washington, D. C.2003: 1-21Google Scholar and 4Barker H.A. Explorations of bacterial metabolism..Annu. Rev. Biochem. 1978; 47: 1-33Crossref PubMed Scopus (9) Google Scholar.1All biographical information on Horace A. Barker was taken from Refs. 3Switzer R.L. Stadtman E.R. Stadtman T.C. Biographical Memoir of H. A. Barker. 84. National Academy of Sciences, Washington, D. C.2003: 1-21Google Scholar and 4Barker H.A. Explorations of bacterial metabolism..Annu. Rev. Biochem. 1978; 47: 1-33Crossref PubMed Scopus (9) Google Scholar.