CHAPTER 4
     PURIFICATION AND IDENTIFICATION OF THE MAJOR PROTEINS OF
  POLYHEDRAL ORGANELLES INVOLVED IN COENZYME B12-DEPENDENT
    DEGRADATION OF 1,2-PROPANEDIOL IN Salmonella enterica SEROVAR TYPHIMURIUM LT2

                                 Introduction

     The vitamin B 12 coenzymes, adenosyl-B12 (Ado-B12) and methyl-B12 (CH3-B12) are required cofactors for at least 15 different enzymes (Schneider and Stroinski 1987a, Roth et al. 1996). These enzymes have a broad but uneven distribution among living forms and are vital to human health, essential to the carbon cycle, and have important industrial applications (Roth et al. 1996). Historically, bacteria have provided excellent model systems for studying vitamins, and recent investigations with several bacterial systems have found the molecular biology of B12-dependent processes to be unexpectedly complex (Stojiljkovic et al. 1995, Roth et al. 1996, Bobik et al. 1999, Sauvageot et al. 2002). One of the most surprising findings in this area has been the identification of a polyhedral organelle involved in coenzyme B12-dependent 1,2-propanediol (PD) degradation by Salmonella enterica (Bobik et al. 1999).

     S. enterica utilizes PD as a carbon and energy source in an Ado-B 12-dependent fashion (Jeter and Roth 1987). Degradation occurs aerobically, or anaerobically if tetrathionate is added as a terminal electron acceptor (Price-Carter et al. 2001). The ability to degrade PD appears to be important to the lifestyle of S. enterica which, including the genes necessary for de novo cofactor synthesis, maintains 40 to 50 genes in order to accomplish this process. Based on biochemical studies, a pathway for PD