¡-Arginine 39 itself has not yet been found in nature, although a ¡-arginine moiety is incorporated into the antibiotics blasticidin S and H [49] from Streptomyces gri-seochromogenes, and in LL-BM547i [50]. The conversion of arginine to ¡-arginine in S. griseochromogenes has been investigated in detail by chemical methods [51, 52]. Administration of (rac)-[3-13C,2-15N]arginine to bacteria cultures and NMR spectroscopic analysis of the isolated blasticidin S revealed the retention of the a-amino group and its intramolecular migration to the ¡ position, suggesting the presence of an arginine 2,3-aminomutase. Further feeding experiments with (3R,2RS)-[3-2H]arginine and (3S,2RS)-[3-2H]arginine revealed that the pro-3R hydrogen from arginine migrates to position 2 in ¡-arginine whereas the pro-3S hydrogen remains at C3. (Scheme 1.6.11). These results are in perfect agreement with those derived from incubation experiments with lysine 2,3-aminomutase. The arginine 2,3-aminomutase might therefore belong to the same enzyme family as the lysine 2,3-aminomutase. The cofactor requirements of the enzyme have not been investigated.

Scheme 1.6.11. Biosynthesis of (S)-b-arginine 38 in Streptomyces griseochromogenes.

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