Clostridium subterminale

In the bacteria Clostridium subterminale SB4 and C. sticklandii (S)-jS-lysine 25 is generated from (S)-lysine by (S)-lysine 2,3-aminomutase [22-24]. 

These experiments do not, nevertheless, enable conclusions to be drawn about which of the hydrogen atoms at C3 is transferred to C2. It therefore remains an open question whether the mutase of the mushroom resembles more the phenylalanine 2,3-aminomutase from Taxus brevifolia or the lysine 2,3-aminomutase from Clostridium subterminale SB4. Because of the lack of any evidence of the occurrence of B12 in higher fungi [65], involvement of B12 in the aminomutase reaction is unlikely. 

So far, two types of aminomutase have been investigated in detail. Lysine 2,3-aminomutase from Clostridium subterminale SB4 is the example par excellence for the SAM-dependent type of aminomutase. Several other enzymes belonging to the same family are known. Examples are biotin synthase [82], pyruvate formate lyase [83, 84], and anaerobic ribonucleotide reductase [85]. 

The initial step in the microbiological metabolism of lysine to acetate, butyrate, and ammonia is the reversible interconversion of L-lysine and L-jS-lysine via exchange of the a-amino group and a /8-proton catalyzed by lysine 2,3-aminomutase (Scheme 49). The reaction has been observed in several species of Clostridium, Nocardia, and Streptomyces (218, 219), but the mechanistic studies have concentrated on the enzyme from Clostridium subterminale SB4, which has been purified and characterized (220). The enzyme is extremely sensitive to reversible oxygen inactivation, with reactivation achieved by anaerobic incubation with a thiol and Fe(II), and a protein-bound Fe(II) is apparently required for activity (220). The exchange reaction is also accelerated by S-... 

LAM from Clostridium subterminale in complex with the substrate crystallizes as a homotetramer with domain-swapped dimers stabilized by structural zinc ions. Each monomer contains one active site, which is a channel defined by a P / a) -crescent and binds a molecule of PLP, a molecule of SAM, and a [4Fe-4S] cluster. In the active site the external aldimine of PLP with lysine, SAM, and the Fe-S cluster lie spatially close (Figure 29), supporting the idea that the formation of the 5 -deoxyadenosyl radical and the abstraction of the... 

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