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Amino Acids↗
Biomedical subjects
G A Sykes
Publications and source records attributed to G A Sykes.
Conformational changes in Chondrus crispus flavodoxin on dissociation of FMN and reconstitution with flavin analogues.
The apoflavodoxin produced by precipitation of Chondrus crispus flavodoxin with trichloroacetic acid migrates as a single molecular species on non-denaturing PAGE, but at a much lower Rm than the flavoprotein. Values of s and D were significantly lower than for the flavodoxin, but their substitution in the Svedberg equation indicated the molecular mass was closely similar to that of the flavodoxin. This was confirmed by meniscus-depletion sedimentation-equilibrium studies. The Stokes radius of the apoflavodoxin was 3.65 nm, compared with 2.33 nm for the flavodoxin, and estimates of frictional coefficient ratio suggested the apoprotein was in extended conformation compared with the roughly globular shape of the flavodoxin. The Ka for FMN binding was 2.8 x 10(8)M, and the electrophoretic and physicochemical properties of the reconstituted flavoprotein were closely similar to those of the native flavodoxin. FAD, iso-FMN and thio-FMN were also bound effectively, but methyl-FMN and riboflavin were bound only weakly, if at all. The reconstituted flavoproteins were active to various extents in mediating electron transfer from NADPH to cytochrome c catalysed by flavodoxin-NADP+ oxidoreductase, the highest activity being with the thio-FMN flavodoxin.
Apoproteins↗
Redox potentials of algal and cyanobacterial flavodoxins.
The redox potentials of flavodoxins from the cyanobacteria Synechococcus PCC 6301 (formerly Anacystis nidulans) and Nostoc strain MAC, and from the red alga Chondrus crispus, were determined by potentiometric titration. For the oxidized-semiquinone interconversion the potentials at pH 7.0 of the three flavodoxins were between -210 and -235 mV, and these were pH-dependent over the range pH 6.9-8.2. For the semiquinone-reduced interconversion the potentials of the cyanobacterial flavodoxins were close to -414 mV, and that for the algal flavodoxin, -370 mV, is the highest reported in this group of flavoproteins.
Cyanobacteria↗
Apoflavodoxin aggregation following dissociation of flavin.
Flavodoxins were isolated for the cyanobacteria Anacystis nidulans and Nostoc strain MAC, and from the red alga Chondrus crispus, and apoflavodoxins prepared by five methods. Gel electrophoretic studies showed that whereas the apoproteins of A. nudulans and Nostoc strain MAC were recovered in monomeric form, the removal of riboflavin 5'-phosphate from C. crispus flavodoxin resulted in extensive aggregation of the apoprotein. In extent and nature this aggregation differed with the dissociating agent used.
Apoproteins↗