IMP DEHYDROGENASE FROM TEA LEAVES AND SUSPENSION-CULTURED CATHARANTHUS-ROSEUS CELLS

The maximum catalytic activities of IMP dehydrogenase (IMPDH) in young tea (Camellia sinensis) leaves and in suspension-cultured Catharanthu s roseus cells were 321 and 48 pkat g-1 fr. wt, respectively. The K(m) values of IMPDH that had been partially purified from tea and from C. roseus were 28 muM and 14 muM, respectively. Both enzymes were inhibi ted by purine nucleotides, especially GMP. The K(i) value of the enzym e for GMP was 170 muM for the enzyme from tea and 67 muM for the enzym e from C. roseus. Metabolites related to the biosynthesis of caffeine had little effect on the activity of the enzyme from either source. Pa rticipation of IMPDH in the biosynthesis of caffeine is discussed.