* To whom correspondence should be addressed.
Received January 28, 2008; Revision received March 19, 2008
Three electrophoretically homogeneous isocitrate lyase (ICL) isoforms were obtained by 4-step purification from corn scutellum (ICL1 and ICL2) and green leaves (ICL). Their physicochemical, kinetic, and regulatory properties were analyzed. The molecular masses of ICL1, ICL2 , and ICL isoforms determined by gel filtration are 164, 207, and 208 kDa, respectively. The proteins have homotetrameric quaternary structure with subunit molecular masses of 43, 48, and 47 kDa for ICL1, ICL2, and ICL, respectively. We found some differences in pH optimum, Km, and regulation by divalent metal cations between ICL1 and ICL2 and significant similarity of ICL2 and ICL. Based on these data, we suggest the participation of these isoforms in metabolic regulation of the glyoxylate cycle, organic acid metabolism during photorespiration in leaves and acidosis in corn seeds.
KEY WORDS: isocitrate lyase, isoforms, electrophoresis, quaternary structure, subunits, glyoxylate cycle, gluconeogenesis