Catabolism of camphor in tissue cultures and leaf disks of common sage (Salvia officinalis)
1992
Funk, C. | Koepp, A.E. | Croteau, R.
(+)-Camphor constitutes nearly 30% of the monoterpenes accumulated in the leaves of common sage (Salvia officinalis), and as the plant approaches maturity the content of this monoterpene ketone decreases by roughly half. Although the ability to catabolize camphor has been demonstrated previously in sage leaf disks, tissue cultures proved to be a more suitable system for examining the responsible degradative pathway. Cell suspension cultures were shown to convert (+)-[3-3H2]camphor, in sequence, to 6-hydroxycamphor, 6-oxocamphor, alpha-campholonic acid, and 2-hydroxy-alpha-campholonic acid, and each intermediate of the pathway was identified by chromatographic and spectroscopic means. This oxidative ring opening sequence resembles the pathway for camphor degradation by the soil diphtheroid, Mycobacterium rhodochrous, that ultimately leads to isoketocamphoric as the last defined metabolite that contains all 10 carbons of the original bicyclic nucleus. Studies with both cell cultures and leaf disks also demonstrated that the catabolism of camphor via 1,2-campholide, a metabolite in sage leaves previously described, was a minor degradative pathway. The first step in the metabolism of camphor was demonstrated in cell-free extracts of the cultured sage cells, and several lines of evidence indicated that this microsomal (+)-camphor-6-exo-hydroxylase is a cytochrome P450-dependent monooxygenase.
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