pathway: Metabolic role of l

nfirmed this suggestion (27-29), but no direct evidence for the ,cific role of the LytB protein has been reported up to now. The nonmevalonate pathway is present in many eubacteria (for ,iew see refs. 9-12). In higher plants, both pathways are operae; while triterpenes including the sterol precursor, cycloartenol, known to be produced by means of the mevalonate pathway in , cytoplasmic compartment of plant cells, a large number of other penes (e.g., mono- and diterpenes) are produced in the plastid mpartment by means of the deoxyxylulose phosphate pathway. e picture is complicated by the exchange of certain terpene :cursors between the two compartments; because of this )sstalk between the two pathways, terpenes synthesized in plass can be derived in part from the cytoplasmically located mevaiate pathway and vice versa. For numerous microbial pathogens such as Enterobacteria and 'cobacterium tuberculosis, the nonmevalonate pathway is the :lusive source of terpenoids. The alternative terpenoid pathway s also been shown to be essential in Plasmodium spp., which is ponsible for more than a million deaths per year (30). Because the enzymes of the nonmevalonate pathway have no hologs in mammalian hosts, they are attractive targets for the velopment of novel antibiotic and/or antiprotozoal agents. Thus, ' further elucidation of the nonmevalonate pathway enzymes pears urgent to provide molecular information for drug design. is article describes the role of the ispH (formerly designated lytB) ne product in the conversion of l-hydroxy-2-methyl-2-(E)tenyl 4-diphosphate into IPP and DMAPP. perimental Procedures