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The system for oxidation of reduced diphosphopyridine nucleotide (DPNH) in mammalian tissue and yeast cells has been studied intensively, and considerable information about it is available. A specific system for oxidation of reduced triphosphopyridine nucleotide (TPNH) has not been demonstrated, although transhydrogenases exist which link TPNH to the DPNH oxidase system (Colowick et al., 1952; Kaplan et al., 1953). TPNH-specific cytochrome c reductase has been isolated from liver (Horecker, 1950), but its importance remains to be determined. Knowledge of bacterial respiratory pathways is quite incomplete. Most microorganisms do not have the conventional complement of cytochromes usually attributed to mammalian and yeast cells; in any given organism one or more of the components may be missing, and only a few microorganisms have a complete system comparable to these cells (Smith, 1953). Pasteurella tularensis contains only cytochromes b, a1, and a2 (Fellman and MIills, 1954 unpublished data). This paper presents data from investigations of the TPNH (glutamic) oxidase system in P. tularensis. The role and involvement of cytochromes, flavoproteins, and cofactors in this terminal oxidative pathway have been studied. MATERIALS AND METHODS The methods of growth, harvest, preparation of sonic extracts, and assay described in a previous paper (Rendina and Mills, 1957) were used. An acetone powder extract of whole cells was prepared as follows: cells from 1 L of broth 1 The work reported here was supported in part by the Chemical Corps, Fort Detrick, Frederick, Maryland, and in part by research grant

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