(+)-Camphor, a major monoterpene of the essential oil of common sage (Salvia officinalis), is catabolized in senescent tissue, and the pathway for the breakdown of this bicyclic ketone has been previously elucidated in sage cell-suspension cultures. In the initial step of catabolism, camphor is oxidized to 6-exo-hydroxycamphor, and the corresponding NADPH-and O,-dependent hydroxylase activity was demonstrated in microsomal preparations of sage cells.Severa1 well-established inhibitors of cytochrome P-450-dependent reactions, including cytochrome c, clotrimazole, and C O , inhibited the hydroxylation of camphor, and CO-dependent inhibition was partially reversed by blue light. Upon treatment of sage suspension cultures with 30 mM MnCI2, camphor-6-hydroxylase activity was induced up to 7-fold. A polypeptide with estimated molecular mass of 58 kD from sage microsomal membranes exhibited antigenic cross-reactivity in western blot experiments with two heterologous polyclonal antibodies raised against cytochrome P-450 camphor-5-exo-hydroxylase from Pseudomonas putida and cytochrome P-450 limonene-6s-hydroxylase from spearmint (Mentha spicata). Dot blotting indicated that the concentration of this polypeptide increased with camphor hydroxylase activity in microsomes of Mn'+-induced sage cells. These results suggest that camphor-6-exo-hydroxylase from sage is a microsomal cytochrome P-450 monooxygenase that may share common properties and epitopes with bacterial and other plant monoterpene hydroxylases.The biosynthetic capacity of plant cell cultures to produce various monoterpenoid, sesquiterpenoid, and diterpenoid substances has been demonstrated; however, the accumulation of monoterpenes in cultured cell systems is only rarely observed (Banthorpe et al., 1986; Charlwood et al., 1989). Studies with undifferentiated suspension cultures of common sage (Salvia officinalis) showed that the enzymes directly responsible for the conversion of the ubiquitous isoprenoid precursor, geranyl pyrophosphate (Fig. 1, structure l)', to (+)-camphor (Z), a major monoterpene of the intact plant, were readily detected during the late logarithmic phase of growth. Yet, no significant accumulation of camphor (C0.3 ng/g fresh