Different Forms of Fructose 1,6-Bisphosphatase in Chlorella

Chlorella kessleri, Fructosebisphosphatase, Superose-FPLC, DEAE-Chromatography, Enzyme Oligomerization In crude extracts of Chlorella kessleri two forms of fructosebisphosphatase can be separated by ion exchange chromatography or by acid precipitation. FBPase I is eluted from DEAE cel­ lulose at 200 m M KC1 and precipitated at pH 4.5, FBPase II is correspondingly eluted at 310 m M KC1 and soluble at pH 4.5. Both enzymes differ in substrate affinity and degree of cooperativity. Based on literature data, FBPase I is assumed to be of cytosolic and FBPase II of chloroplastic origin. The mole mass of FBPase I is identical (51-65 kDa) at pH 6.5 and pH 8.5. That of FBPase II is however, about four times larger at pH 6.5 (257 kDa) than at pH 8.5 (67 kDa). Other pH values have only been tried with crude cell extracts in which still larger mole masses of FBPase resulted at more acidic pH (1349 kDa at pH 6.0). The lower mole mass form of FBPase II shows three times higher catalytic activity. Reducing agents, such as DTT, also increase the activity of FBPase II in vitro. In vivo, alkalization and production of reducing power occurs in the chloroplast stroma du­ ring illumination. If the above alterations exist in vivo, they would be a means to activate FBPase in the light. Oligomerization of FBPase II to aggregates with altered catalytic activities and kinetic prop­ erties is discussed as result of the action of specific wavelengths and to be responsible for differ­ ences in carbohydrate metabolism of Chlorella exposed to red or blue light.