Hydroperoxide cyclase

In cereals the cleaving enzyme E2 is transformed into a hydroperoxid-isomerase and into a hydroperoxid cyclase producing prostaglandine-like components. 

The product of hydroperoxide cyclase, 12-oxo-PDA, is a key intermediate in the biosynthesis of jasmonic acid (17) (Fig. 2). First, the ring double bond of 12-oxo-PDA is reduced by NADPH in the presence of 12-oxo-PDA reductase (18). Then, after three cycles of 8-oxidation of the carboxyl side chain, jasmonic acid is formed. 

Figure 8.6 A diagram of the oxylipin pathway. LOX lipoxygenase AOS allene oxide synthase HPL hydroperoxide lyase AOC allene oxide cyclase OPDA Reductase 12-oxo-phytodienoic acid-10,11-reductase.

Fig. 8. Metabolism of 18 3 fatty acid to oxylipins. I. Lipoxygenase 2, alleneoxide synthase 3, allene oxide cyclase 4, 12-oxo-phytodienoic acid reductase, -oxidation 5, hydroperoxide lyase.

Squalene 2,3-epoxide has been isolated from the green alga Caulerpa prolifera. Oxidation of squalene with t-butyl hydroperoxide in the presence of Mo02(acac)2 and di-isopropyl (+)-tartrate gave the 2,3-epoxide (31%) with an induced asymmetry of about 14% in favour of the (35)-isomer. The ability of oxidosqualene cyclases to accept unnatural precursors has been further extended by the observation that lanosterol cyclase from rabbit liver converts the synthetic epoxide (1) into the jS-onocerin derivative (2). An authentic sample of (2) was prepared by sodium cyanoborohydride reduction of /3-onoceradione... 

Graff G, Stephenson JH, Glass DB, Haddox and Goldberg W) Activation of soluble splenic guanylate cyclase by prostaglandin endoperoxides and fatl acid hydroperoxides. J Btol Ckm 253 7662-7776, 1978. 

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