Pyridine‐Nucleotide Transhydrogenase

• Published in: European journal of biochemistry Vol. 24; no. 1; pp. 46 - 54
• Main Authors: Broek, Hendricus W. J., Breemen, Jan F. L., Bruggen, Ernst F. J., Veeger, Cornelis
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.1971
• ISSN: 0014-2956; 1432-1033
• DOI: 10.1111/j.1432-1033.1971.tb19653.x

1 Electron‐microscopic investigations confirmed the inhomogeneity of the transhydrogenase preparations from Azotobacter vinelandii. Representative preparations contain helical‐like structures up to 1000 nm apart from large amounts of shorter rod‐like structures and fragments. The diameter of both the threads and rods is 11.6–12.0 nm. The fragments do not show a clearcut substructure and they possibly represent projections of spherical particles; the thread‐like structures may represent spiral‐like structures. 2 Addition of NADP+ to the enzyme solution results in fragmentation of the thread‐like structures, but the dissociation is never complete. Extensive removal of NADP+ results in more homogeneous preparations with structures up to 1500–1800 nm in length. The ratio NADPH/NADP+ seems to be regulatory for the length of the structures. No clear‐cut dissociation effect is obtained with other nucleotides. 3 The presence of ladder‐like structures with constituents very similar to the thread‐like structures of the transhydrogenase and the tetramer‐like structures found in preparations of pyruvate‐dehydrogenase complex is discussed in terms of a multi‐enzyme complex. The ladderlike structures resist the influence of the different nucleotides. 4 Ammonium‐sulfate‐crystalline suspensions of the enzyme show regular “stacked discs” structures; solubilisation results in the appearance of the thread‐like transhydrogenase structures, fragments and rosettes, but no close interaction between the different species could be established. 5 From examination of the different purification stages it is concluded that the thread‐like transhydrogenase structure is not an artefact due to the method of purification. The observations point to a relation between the presence of the thread‐like structures, the concentration of the transhydrogenase and the removal of the pyruvate‐dehydrogenase complex.