Abstract
The maximum catalytic activity of pyrophosphate: fructosc-6-phosphate 1-phosphotransferase (PPi-PFK) was approximately three fold greater than that of ATP: fructosc-6-phosphate 1-phosphotransferase (ATP-PFK) in Catharanthus roseus cells at any stage of culture. The levels of both enzymes increased after subculture of the cells, reached their maximum levels on day 3-4, and then decreased. PPi-PFK partially purified from Catharanthus roseus required fructose-2,6-bis- phosphate (F2,6BP) for its activity. The Ka value of the enzyme for F2,6BP was 26 nᴍ. The Km values for fructose-6-phosphate (F6P) and sodium pyrophosphate (PPi), at physiological pH (7.2) in the presence of 1 µᴍ F2,6BP, were 0.59 mᴍ and 48 µᴍ, respectively. Intracellular levels of PPi and F6P varied from 17-71 nmol and from 37-65 nm per g fresh weight of the cells during culture. These results suggest that PPi-PFK is functional in Catharanthus roseus cells in vivo. The role of PPi-PFK in carbohydrate metabolism in heterotrophic, cultured plant cells is discussed.
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