Cathenamine synthase

Strictosidine synthase 2 strictosidine glucosidase 3 cathenamine synthase... 

Dehydrogeissoschizine may also be converted to cathenamine in a reaction catalyzed by cathenamine synthase (CS) [24]. This compound is the basis for the formation of ajmaUcine by the action of the enzyme cathenamine reductase (CR), and then, ajmalicine is thought to be oxidized to serpentine by class 111 peroxidases (Prx) localized in the vacuoles, with its production being strongly regulated by light (Scheme 4.4, [25]). 

The formation of ajmalicine from the carbinolamine or cathenamine requires a reduction. Hemscheidt (217) and Stdckigt et al. (222) described an enzyme cathenamine reductase (CR), which used cathenamine as substrate and NADPH as cofactor, yielding ajmalicine and 19-epi-ajmalicine. Hemscheidt and Zenk (223) reported partial purification of an NADPH-dependent tetrahydroalstonine synthase (THAS) from C. roseus cell cultures. This enzyme only yields tetrahydroalstonine, and the substrate was the iminium form of cathenamine. The Km for this substrate is 62 /nAf. The molecular mass of the enzyme was estimated to be 81 kDa. 

Fig. 8.5 Compartmentation of alkaloid biosynthesis in Cathamnthus roseus. AS anthianilate synthase, CR NADPH cathenamine reductase, DAT deacetylvindoline 17-O-acetyltransferase, ER endoplasmic reticulum, GlOH geraniol 10-hydroxylase, GAP glyceraldehyde-3-phosphate, NMT S-adenosyl-L-methionine methoxy-2, 16-dihydro-16-hydioxylagersonine-lV-methyltransferase, OHT desacetoxyvindoline-4-hydroxylase, SGD strictosidine -glucosidase, STR strictosidine synthase TDC tryptophan decarboxylase, THAS NADPH tetrahydroalstonine reductase (Adopted from Ref. [10])... 

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