PUB - Publikationen an der Universität Bielefeld

Total activity of FBPase of Chlorella kessleri grown either in blue or in Ted light of equal fluence rates differs (26.8 and 61.0 nmol.min(-1).mg protein(-1)) in crude cell extracts prepared at pH 8.5. The difference largely depends on FBPase II, an enzyme species assumed to be located in the chloroplast. FBPase II is strongly influenced by reducing agents. Addition of DTT, however, does not compensate for the difference in activities. Although it leads to a higher increase (197%) in the activity of the enzyme from blue than in that of the enzyme from red light conditions, the final activities (79.7 and 133.1 nmol.min(-1).mg protein(-1)) still differ by a factor of 1.67. In contrast to alkaline conditions the activity is approx. equal when crude cell extracts are prepared at pH 6.0. It is 62.7 nmol.min(-1).mg protein(-1) in blue light and 70.7 in red light. Under these conditions DTT enhances both activities equally (189 and 201 nmol.min(-1).mg protein(-1)). These results indicate that the observed difference in enzyme activity at pH 8.5 does not result from different enzyme quantities. At pH 8.5 the mole mass of FBPase II is 88 kDa, while it is 1349 kDa at pH 6.0 under both light conditions. The smaller mole mass represents the monomeric form of the enzyme. The previously assumed pH-dependent oligomerization/dissoziation [8], which is generally proven, is therefore not responsible for the different activities of the enzyme from cells grown in red or in blue light. However, the monomeric form seems to possess a higher stability when prepared from cells from red light conditions. The different stability and activity of FBPase II under alkaline conditions are discussed in context with an altered carbohydrate metabolism in Chlorella kessleri grown autotrophically in different wavelengths of light.