d-dopachrome into 5,6-dihydroxyindole. The enzyme source is not clear from Chemical Abstracts; it is claimed to be a rat enzyme, but it may be the same as that described in another publication, found in human lymphocytes. The latter is a macrophage migration inhibition factor in addition to its tautomerase activity [J475, J514].
L-Dopachrome tautomerase (E C. 188.8.131.52)
Mouse melanoma enzyme forms 5,6-dihydroxyindole-2-carboxylate as the initial product. The apoenzyme is activated by Zn2 + , but not by Fe2+ or Cu2+ [H338].
Locusta migratoria enzyme, dopachrome conversion factor, (dopachrome D-isomerase, E.C. 184.108.40.206), molecular weight 85000, forms 5,6-dihydroxyindole from l-dopachrome; it also acts on l-dopachrome methyl ester and methyldopachrome, but not on their d-isomers or dopaminechrome [J842].
Bombyx mori dopa quinone imine conversion factor, optimum pH 7.5-9, forms 5,6-dihydroxyindole from l- (but not d-) dopachrome [H429].
Aromati/ation of lindane
Lindane (the isomer used is not clear, but is presumed to be the active g-isomer) is converted into 1,2,4-trichlorobenzene in bean, and into 1,2,3- and 1,2,4-trichlorobenzene in Zea mays [A766].
1.2 Formation of carbon ring systems
Naphthalene derivatives formed from o -succinylbenzoate a. Naphthoate synthetase (E.C. 220.127.116.11)
E. coli enzyme, molecular weight 45 000, requires acetyl CoA, ATP and Mg2+ to form
1,4-dihydroxy-2-naphthoate. In crude extracts, the addition of farnesyl pyrophosphate results in the formation of menaquinone-3 at the expense of 1,4-dihydroxy-2-naphthoate [A2774]. Studies with Mycobacterium phlei, E. coli and Galium mollugo have found that o -succinylbenzoyl CoA is formed as an intermediate [C337, E594]. M. phlei enzyme has a molecular weight of 44 000 and optimum pH 6.9. The succinyl carboxyl is retained as the carboxyl group in 1,4-dihydroxy-2-naphthoate [A2943].
b. Phylloquinone formation
In Zea mays phylloquinone is formed from o-succinylbenzoate, retaining its structural integrity [A175, A3973].
c. 1,4-Naphthoquinone formation
Juglans regia catalyzes the formation of 1,4-naphthoquinone and juglone (5-hydroxy-1,4-naphthoquinone) [A3470]. 1,4-Dihydroxy-2-naphthoate is an intermediate in juglone formation as well as in lawsone (2-hydroxy-1,4-naphthoquinone) formation [A1639].
Cannabis sativa enzyme, molecular weight 74 000 and pI 6.1, catalyzes the ring closure of cannabigerolate and cannabinerolate into cannabidiolate. The enzyme is not an oxygenase or peroxidase; presumably it is a dehydrogenase, which forms a cyclohexene ring system [J205].
Pinosylvin (3,5-dihydroxystilbene) synthase
Pine (Pinus sylvestris) enzyme catalyzes the condensation of cinnamoyl CoA with malonyl CoA to form a second aromatic ring. With p -coumaroyl CoA the hydroxylated analogue, resveratrol is formed [B313].
Dioscorea shows similar metabolic reactions with cinnamoyl CoA, m -hydroxyphenylpropionyl
CoA and analogues; the products, such as resveratrol and pinosylvin are intermediates in the formation of hircinol and batatasins [D136].
This reaction occurs poorly in Barlia long-ibracteata with cinnamoyl CoA, m -coumaroyl CoA and p -coumaroyl CoA as substrates. The corresponding dihydro substrates form the analogous bibenzyls, but more effectively [C734].
Epipactis palustris enzyme, molecular weight 85000, shows a similar specificity and co-substrate requirement to those for the above enzymes [G138].
Barlia longibracteata enzyme acts on CoA conjugates of 3-phenylpropionic acid; the m - and p -hydroxy analogues also form the corresponding bibenzyls [C734].
Bletilla striata enzyme is a dimer, monomeric molecular weight 46 000, which condenses m -hydroxyphenylpropionyl CoA with malonyl CoA to form 3,3',5-trihydroxybibenzyl [H101].
Epipactis palustris enzyme, molecular weight 85 000 acts on m-hydroxyphenylpropionyl CoA; a good additional substrate is phenylpropionyl CoA, which yields dihydropinosylvin, but the corresponding cinnamoyl CoAs are poor substrates [G138]. This distinguishes the enzyme from stilbene synthase, which it closely resembles.
This reaction is the first step in the reaction sequence that leads to the formation of polycyclic flavonoid plant pigments from cinnamates, forming a second aromatic ring.
Buckwheat enzyme is a homodimer, molecular weight 83 000, pI 5.2 and optimum pH 8.0. It condenses malonyl CoA with p -coumaroyl CoA, feruloyl CoA and caffeoyl CoA [E180].
Cephalocereus enzyme converts cinnamoyl CoA into 2',4',6'-trihydroxychalcone [H633].
Daucus carota enzyme exhibits optima at pH 7.9 and 6.8 with p -coumaroyl CoA and caffeoyl CoA, respectively [D698].
Dianthus caryophyllus enzyme exhibits pH optima of 8.0 and 7.0 withp-coumaroyl CoA and caffeoyl CoA, respectively [C392].
Glycine max enzyme, molecular weight 75 000, is composed of three isozymes, pI 5.45 (main), 5.35 and 5.5, and pH optima of 7.5 and 6.5 with p -coumaroyl CoA and caffeoyl CoA, respectively [E579]. A reductase is involved in the reaction sequence [E661].
Glycyrriza echinata enzyme acts on p-coumaroyl CoA, malonyl CoA and NADPH [E619].
Parsley enzyme, molecular weight 77 000 appears to be a dimer (monomeric molecular weight 42 000) with p -coumaroyl CoA and malonyl CoA as substrates [B352, K808].
Phaseolus vulgaris enzyme, molecular weight 77000 and optimum pH 8.0, acts on malonyl CoA and p -coumaroyl CoA [C813].
Rye enzyme requires malonyl CoA as co-substrate, and acts on p -coumaroyl CoA (optimum pH 8) and caffeoyl CoA (optimum pH 6.5) to form 2',4,4',6-tetrahydroxy- and 2',3,4,4',6'-pentahydroxychalcones (precursors of naringenin and eriodictyol), respectively [E662].
Spinach enzyme is composed of two isozymes, pH optimum 7.5-8, with p-coumaroyl CoA, feruloyl CoA and caffeoyl CoA as substrates [D596].
A tulip anther enzyme, molecular weight 55000 and optimum pH 8.0 acts on p -coumaroyl CoA, feruloyl CoA and caffeoyl CoA to form naringenin, homoeriodictyol and eriodictyol respectively; it is inhibited by CoA, flavanones and thiols. The preparation was claimed to be free from chalcone-flavanone isomerase activity; the expected chalcone intermediates were not detected [A3792]. A similar enzyme found in Haplopappus gracilis, optimum pH about 8 for p-coumaroyl CoA, and 6.5-7 for caffeoyl CoA was called flavanone synthase. The reaction was not stoichiometric, with small amounts of by-products such as benzalacetones being formed [A3362]; a similar series of reactions was found in Petroselinum crispum [A2618]. These publications all come from early studies on the enzyme system, and despite the claims that chalcone-flavanone isomerase activity was
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