We have demonstrated that cellular localization of aldolase B and its interaction with fructose-1,6-bisphosphatase-1 (FBPase-1) is modulated by the metabolic conditions. These results show a new level of regulation for aldolase B and FBPase-1 in a cellular context.

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Pig kidney fructose‐1,6‐bisphosphatase is a homotetrameric enzyme which does not contain tryptophan. In a previous report the guanidine hydrochloride‐induced unfolding of the enzyme has been described as a multistate process [Reyes, A. M., Ludwig, H. C., Yañez, A. J., Rodriguez, P. H and Slebe, J. C. (2003) Biochemistry 42, 6956–6964]. To monitor spectroscopically the unfolding transitions, four mutants were constructed containing a single tryptophan residue either near the C1–C2 or the C1–C4 intersubunit interface of the tetramer. The mutants were shown to retain essentially all of the structural and kinetic properties of the enzyme isolated from pig kidney. The enzymatic activity, intrinsic fluorescence, size‐exclusion chromatographic profiles and 1‐anilinonaphthalene‐8‐sulfonate binding by the mutants were studied under unfolding equilibrium conditions. The unfolding profiles were multisteps, and formation of hydrophobic structures was detected. The enzymatic activity of wild‐type and mutant FBPases as a function of guanidine hydrochloride concentration showed an initial enhancement (maximum ∼ 30%) followed by a biphasic decay. The activity and fluorescence results indicate that these transitions involve conformational changes in the fructose‐1,6‐bisphosphate and AMP domains. The representation of intrinsic fluorescence data as a ‘phase diagram’ reveals the existence of five intermediates, including two catalytically active intermediates that have not been previously described, and provides the first spectroscopic evidence for the formation of dimers. The intrinsic fluorescence unfolding profiles indicate that the dimers are formed by selective disruption of the C1–C2 interface.

Bacterial communities of Antarctic marine macroalgae remain largely underexplored in terms of diversity and biotechnological applications. In this study, three Antarctic subtidal macroalgae (Himantothallus grandifolius, Pantoneura plocamioides and Plocamium cartilagineum), two of them endemic of Antarctica, were investigated as a source for isolation of agar-degrading bacteria. A total of 21 epiphytic isolates showed agarolytic activity at low temperature on agar plates containing agar as the sole carbon source. 16S rRNA identification showed that the agar-degrading bacteria belonged to the genera Cellulophaga, Colwellia, Lacinutrix, Olleya, Paraglaciecola, Pseudoalteromonas and Winogradskyella. The agarase enzyme from a potential new species of the genus Olleya was selected for further purification. The enzyme was purified from the culture supernatant of Olleya sp. HG G5.3 by ammonium sulfate precipitation and ion-exchange chromatography. Molecular weight of the agarase was estimated to be 38 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified enzyme exhibited activity at 4 °C, retaining > 50% of its maximum activity at this temperature. This is the first study reporting the phylogeny of agar-degrading bacteria isolated from Antarctic subtidal macroalgae and the results suggest the huge potential of Antarctic algae-associated bacteria as a source of cold-active hydrolytic enzymes of biotechnological interest.

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