Oxidation hydroxylamine biosynthesis

A question occurs as to why the bacterial enzyme has such a complicated structure, because hydroxylamine is oxidized to nitrite by the catalysis of ferric ion under aerobic conditions. In the nonenzymatic reaction, molecular oxygen is incorporated into nitrite formed by the oxidation of hydroxylamine, while the oxygen atom of water is incorporated into nitrite formed by the enzymatic oxidation of hydroxylamine (see below) (Yamanaka and Sakano, 1980 Andersson and Hooper, 1983). The mechanism in the bacterial oxidation of hydroxylamine will have been devised to reserve efficiently the energy of the reaction for the biosynthesis of adenosine triphosphate (ATP). 

Two of the four electrons generated from hydroxylamine oxidation are used to support the oxidation of additional ammonia molecules, while the other two electrons enter the electron transfer chain and are used for CO2 reduction and ATP biosynthesis [153,154]. 

Yamazaki et al. (221) have postulated that the tryptoquivalines may be biogenetically derived from four amino acids tryptophan, anthranilic acid, valine and alanine. Deoxynortryptoquivalone is thought to be the first compound formed in the biosynthesis of the tryptoquivaline series. Oxidation of the secondary amine in this compound to a hydroxylamine would result in nortryptoquivalone. Oxidative loss of the side-chain would lead to FTE or FTJ. Alternatively, reduction of the side-chain carbonyl group would afford nortryptoquivaline. The geminal dimethyl group at C-15 may result from incorporation of a Cj-unit into deoxynortryptoquivalone or from the direct participation of methylalanine rather than alanine in the initial step of the biosynthesis. 

The biogenesis of the N-hydroxyamide bond is an interesting problem 115). That it may involve oxidation of the a- or co-amine group of an amino acid to a hydroxylamine derivative (Scheme 14, path a) was observed in the biosynthesis of ferrichrome (5) 116), hadacidin (13) (25, 117) and aerobactin (8) 118). 

To more directly assess the role of octanal and 1-octanol in /2-heptane biosynthesis, xylem sections were incubated with 1-octanol and [ " CJoctanal. Incubation of xylem sections with 10 dpm octanal resulted in the incorporation of into /2-heptane, although the majority of radiolabel was recovered as 1-octanol. Incubation of xylem sections with 10 dpm 1-octanol also resulted in incorporation of radiolabel into /2-heptane, and a small amount of radiolabel was incorporated into octanal. To determine whether 1-octanol is first oxidized to the aldehyde before conversion to n-heptane, xylem sections were co-incubated with 10 dpm 1-octanol and 500 mM hydroxylamine. No radiolabel was incorporated into /2-heptane, but was incorporated into octyl oximes. 

These novel metabolites may be derived from four amino acids tryptophan, anthranilic acid, valine, and alanine (or methylalanine). Deoxynor-tryptoquivalone (43) may be the first metabolite formed in the pathway of the tryptoquivaline biosynthesis. By oxidation of the secondary amine to the hydroxylamine, nortryptoquivalone (= tryptoquivalone) (32) would be formed from 43. If the isobutyl side chain is lost by further oxidation, tryptoquivaline J (39) and E (34) would be derived from these tryptoqui-valones, respectively. On the other hand, if reduction occurred on the carbonyl in the side chain, deoxynortryptoquivaline (42) and nortrypto-quivaline (FTD) (40) would be derived, respectively, from these tryptoqui-valones. The geminal dimethyl group at position 15 appeared to be formed by the participation of methylalanine in the biosynthesis, and the actual incorporation of " C-labeled methylalanine into tryptoquivaline (FTC) and tryptoquivaline I has been demonstrated (M. Yamazaki, unpublished work). 

---