Tryptamine and tryptophan hydroxylation

decline to the adult level. In heart the activity increases fourfold between birth and weaning, and then remains constant [A1700]. The enzyme has also been detected in rat stomach, heart, stellate ganglion, superior cervical ganglion and salivary gland as well as adrenal [A368, H620].

In dog, hypotension produced by haemorrhage raises plasma DBH activity by 40 per cent [A3576].

Hen adrenal enzyme appears to be a homo-tetramer, molecular weight 320 000 and optimum pH 5-6, with subunits linked by disulphide bridges. It requires ascorbate (ferrocyanide can act as substitute) and fumarate (acetate is a poor substitute). The product from substrate b-labelled with tritium retains an excess of label. Kinetic studies have suggested a ping-pong mechanism [C56].

Opuntia converts N-methyltyramine into normacromerine (N-methyl-3,4-dimethoxyphenylethanolamine) [A3977].

occur with, for instance, indole-3-propionate or peptide-linked tryptophan [A3007]. During the reaction an oxygen atom is introduced from water, but not from molecular oxygen; oxygen can be replaced by other electron acceptors. The reaction produces an olefinic intermediate that is then hydrated, possibly spontaneously [A3148].

NADPH-dependent L-phenylalanine monooxygenase

Carica papaya enzyme is found only in leaves. It is highly specific; other phenylalanines are not substrates. The reaction involves oxidative decarboxylation to form benzylaldoxime [H947].

Mandelic acid formation from phenylacetic acids

Tryptamine and tryptophan P-hydroxylation

An enzyme in beef adrenal medulla and in most rat tissues acts on tryptamine; it is unclear whether this has any physiological role [B469].

Pseudomonas indole-3-alkane a-hydroxylase (tryptophan 2?-dioxygenase, E.C. acts on tryptamine to form (R)-b-hydroxytryptamine, removing the pro-S hydrogen from C-2 of the side chain. It also acts on tryptophan methyl ester and dl-homotryptophan. A mixture of (2S, 3R)- and (2R, 3S)-b-methyltryptophan is also hydroxylated, but a mixture of (2R, 3R)- and (2S, 3S)-b-methyltryptophan is inactive [B84]. The molecular weight of the enzyme is 250 000, pI 4.8 and optimum pH about 4. Its amino acid composition has been determined, and it contains 0.8 mol Fe/mol. Cyanide and hydroxylamine are inhibitory. A range of tryptophans and tryptamines as well as indoles with 3-alkyl moieties are also substrates. l-Tryptophan is hydroxylated and decarboxylated to b-hydroxytryptamine, with decarboxylation apparently as the second reaction step. Decarboxylation does not


Substrates include phenylacetate and p -hydroxyphenylacetate. Species in which the reaction has been detected include plants (barley, wheat, parsley and Glycine max) and microorganisms (Aspergillus and Pseudomonas) [A329, A2691, A3594, G929].

Hydroxyphenylacetonitrile 2-monooxygenase

Etiolated sorghum seedling enzyme requires oxygen and NADP to form the corresponding mandelonitrile [K711].

Hydroxylation of nuclear methyl groups

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