Geranoyl-CoA carboxylase: A novel biotin-containing enzyme in plants

Geranoyl-CoA carboxylase (EC 6.4.1.4) is a biotin-containing enzyme previou sly described in two genera of bacteria. Here we report the presence of ger anoyl-CoA carboxylase in kingdom Plantae, Geranoyl-CoA carboxylase was puri fied 180-fold from maize leaves. The enzyme has a biotin-containing subunit of 122 kDa. The pH optimum for activity is 8.3. The apparent K-m values fo r the substrates geranoyl-CoA, bicarbonate, and ATP are 64 +/- 5 mu M, 0.58 +/- 0.04 mM, and 8.4 +/- 0.4 mu M, respectively, Subcellular fractionation s indicate that geranoyl-CoA carboxylase is located in plastids. Geranoyl-C oA carboxylase activity is ubiquitous in organs of monocots and dicots and varies with development. We postulate that geranoyl-CoA carboxylase plays a n important role in isoprenoid catabolism in plants, in a pathway analogous to that shown in Psuedomonas sp. In plants, this catabolic pathway would r equire the interaction of at least three subcellular compartments (plastids , microbodies, and mitochondria) and two biotin-containing enzymes, geranoy l-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase. (C) 1999 Academic P ress.