Fructose‐1,6‐bisphosphatase from Synechococcus leopoliensis

Abstract

Extracts of Synechococcus leopoliensis(Anacystis nidulans) contain two forms of D‐fructose‐1,6‐bisphosphatase(EC 3.1.3.11) previously designatedas forms A and B [Gerbling, K.‐P., Steup, M., and Latsko, E. (1984) Arch. Microbiol . 137, 109–114]. Form B, which probably represents the mahor part of the total extractable fructose‐1,6‐bisphosphatase activity, has been purified to apparent homogeneity. Gel filtration, non‐denaturing polyacrylamide gel electrophoresis, and cross‐linking with bis(sulfosuccinimidyl) suberate revealed that the fructose‐1,6‐bisphosphatase B exists in either a dimeric or in a tetrameric subform, depending upon the absence or presence of fructose‐1,6‐bisphosphate and Mg 2+ . The dimer–tetramer interconversion was readily reversible. The results provide evidence for a two‐step activation of fructose‐1,6‐bisphosphatase B involving the reduction of the dimeric subform and the subsequent substrate‐dependent conversion of the reduced dimer to a reduced tetramer, which is the only catalytically active state. In contrast to form B, no substrate‐dependent interconversion was detected with form A from S. leopoliensis .