Lysine 2,3-aminomutase

Studies on three different iron-sulfur enzyme systems, which all require S-adenosyl methionine—lysine 2,3-aminomutase, pyruvate formate lyase and anaerobic ribonucleotide reductase—have led to the identification of SAM as a major source of free radicals in living cells. As in the dehydratases, these systems have a [4Fe-4S] centre chelated by only three cysteines with one accessible coordination site. The cluster is active only in the reduced... 

Cosper NJ, Booker SJ, Ruzicka FJ, et al. 2000. Direct FeS cluster involvement in generation of a radical in lysine 2,3-aminomutase. Biochemistry 39 15668-73. 

LYSINE 2,3-AMINOMUTASE LYSINE 6-AMINOTRANSFERASE LYSINE DECARBOXYLASE... 

KYNURENINE AMINOTRANSFERASE LEUCINE AMINOTRANSFERASE LYSINE 2,3-AMINOMUTASE LYSINE 6-AMINOTRANSFERASE LYSINE DECARBOXYLASE METHIONINE y-LYASE ORNITHINE AMINOTRANSFERASE PHENYLALANINE DECARBOXYLASE PHOSPHATIDYLSERINE DECARBOXYLASE... 

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]. 

Recently, a new SAM dependent lysine 2,3-aminomutase was detected and characterized in Bacillus subtilis. Unlike the enzyme from C. subterminah SB4, the enzyme in B. subtilis apparently consists of four identical subunits each with a molecular mass of 54 kDa [30]. A PLP binding motif was identified in this amino-mutase that is also highly conserved in other lysine 2,3-aminomutases [31]. 

The stereochemistry of the reaction catalyzed by the lysine 2,3-aminomutase in C. subterminah SB4 was elucidated in detail by Aberhardt and Gould [32]. Incubation experiments with cell-free extracts of C. subterminah SB4 and (2RS)-[3-13C,2-lsN]lysine and NMR spectroscopy of the isolated /Mysine as the di-N-phthaloyl ethyl ester derivative revealed that the amino group migrates in an intramolecular reaction to position 3S in /Mysine 25. 

Scheme 1.6.7. Reaction mechanism for generation of (S)-/7-lysine catalyzed by lysine 2,3-aminomutase.

The reaction mechanism outlined was confirmed by direct observation of the jl-lysyl-PLP radical 29 by EPR methods [37]. A strong signal was detected in the EPR spectrum by incubation of lysine 2,3-aminomutase with a-lysine and SAM and subsequent freezing in the steady state with liquid N2. The presence of a /Mysine-... 

Scheme 1.6.8. Incubation of 4-thialysine with lysine 2,3-aminomutase generates 4-thialysyl-PLP radicals.

This reaction mechanism seems not to be restricted to the lysine 2,3-aminomutase itself. The cobalamin-dependent lysine 5,6-aminomutase and the ornithine 4,5-aminomutase from C. sticklandii follow apparently the same reaction mechanism except that they need Bn instead of SAM as cofactor. 

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. 

Reaction Mechanism Although the /Mysine 5,6-aminomutase requires cobalamin as cofactor instead of SAM its reaction mechanism seems to be similar to that of the lysine 2,3-aminomutase [73], Experiments with tritium-labeled lysine and B12 showed that Bn is directly involved in the hydrogen shift from position 5 in d-... 

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]. 

Interestingly, all known cobalamin-dependent aminomutases seem to catalyze a shift of the co amino group whereas the SAM dependent lysine 2,3-aminomutase catalyzes the shift of the a amino group. The latter is true for phenylalanine 2,3-aminomutase in Taxus brevifolia and tyrosine 2,3-aminomutase in Cortinarius vio-... 

Figure 9.50 Typical lysine 2,3-aminomutase run. (A) Initial incubation mixture (t = 0), (f ) Analysis after incubation for 135 minutes. (For quantitation, peak areas are determined the /B peak area is multiplied by 1.85, and total, (1.85 X 0) + a), normalized to 100%. (From Aberhart, 1988.)...

Figure 7. UV-visible spectrum of lysine 2,3-aminomutase. Adapted from reference 2 with permission from the Journal of Biological Chemistry.

Figure 8. Low-temperature EPR spectrum of As-isolated lysine 2,3-aminomutase. (Top) Actual spectrum (bottom) simulated spectrum. Adapted from reference 24 with permission from the American Chemical Society.

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