Calcium-dependent catabolism of pheophorbide a in tomato fruit

摘要

An enzyme which degraded pheophorbide a (Pheid a), a chlorophyll (Chl) catabolite, was found in a crude extract prepared from tomato fruits. Application of 10 mM CaCl2 strongly enhanced the enzyme activity. In the presence of EGTA, the enzyme activity was low and activation of enzyme by CaCl2 did not occur. An inhibitor of calmodulin, trifluoperazine (1 mM) inhibited the enzyme activity, and CaCl2-activation of the enzyme. ATP (5 mM) enhanced the enzyme activity as strongly as did CaCl2. Effects ofATP and CaCl2 were not additive. Inhibitors of protein kinases, H-7 and KN-62, fully reversed the activation of the enzyme by CaCl2. It is concluded that the effects of ATP and CaCl2 on the enzyme activity are mediated by protein kinases that are activated by calcium, utilizing ATP as the phosphate donor. Calmodulin is likely to be involved in the process(es). In addition, this enzyme was inactivated by 2,2'-bipyridyl and salicylic acid. The products of Pheid a degradation in this system were fluorescent compounds according to a rapid scanning of 3-D fluorescent spectrum measurement. They were designated as Tom-FCCs (tomato fluorescence chlorophyll catabolites). Tom-FCCs had the strongest intensity of fluorescence near 300 nm, and emission wavelengthsat 355 and 435 nm. In the presence of CaCl2, production of Tom-FCCs was enhanced, providing evidence that the final step in Chl degradation is regulated by calcium and protein kinase in vitro.