Brevibacterium ammoniagenes manganese

The first bona fide MnRNR, isolated from Corynebacterium (formerly Brevibacterium) ammoniagenes, was reported about 10 years ago [122], The MnRNR R1 protein is monomeric (dimeric in E. coli) [123]. A dinuclear Mnm—0—Mnm unit was believed to be present at its active site (cf. oxidized E. coli RNR), and its sensitivity to hydroxyurea (a radical scavenger) suggested a mechanism similar to that of its iron counterpart. However, no tyrosyl radical EPR signal was observed from the MnRNR, casting doubts about the redox role of the manganese center [118], Very recently, however, a stable EPR signal, which is inhibited by hydroxyurea and correlates directly with enzymatic activity, has been detected [124],... 

The third class of reductases apparently requires manganese for activity, although few other characterizations have been performed. This enzymic activity is found solely in bacteria, specifically in Brevibacterium ammoniagenes, Ar-throbacter, Micrococcus luteus, and Nocardia opaca (37, 38). 

The need for divalent manganese in cell proliferation of certain gram-positive bacteria has long been known but its involvement in ribonucleotide reduction was recognized only recently. Strains like Brevibacterium ammoniagenes or Micrococcus luteus cease to synthesize DNA (but not RNA or protein) in manganese-free fermentation... 

Table 1. Manganese dependence of DNA synthesis (adenine incorporation in vivo) and ribonucleotide reductase activity in Brevibacterium ammoniagenes ...

Additional support for the Mn specificity of native B. ammoniagenes ribonucleotide reductase is provided by its inhibition by cyanide (Fig. 5). The iron- and B 12-enzymes are not affected by cyanide which forms cyano and cyanoaquo complexes with Mn" but not with Fe or Fe" " " under typical enzyme assay conditions at ambient temperature. We thus believe that manganese in the Brevibacterium enzyme system is the functional, catalytic counterpart of iron found in E. coli and eukaryotic ribonucleotide reductases. The nature of Mn -protein interaction remains to be studied after further purification. 

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