CHANGES IN THE STRUCTURE OF PYRUVATE-DEHYDROGENASE COMPLEX-INDUCED BYMONOVALENT AND DIVALENT IONS

The activity of pyruvate dehydrogenase complex purified from pig kidne y cortex was affected by various mono- and di-valent ions and changes in ionic strength. The fluorescence emission spectrum of PDC exposed t o 0.04 M ionic strength and excited at 280 nm exhibited a maximum at 3 34 nm; the fluorescence intensity of PDC appeared to depend upon the i onic strength and the K+ and Na+ content of the incubation buffer. Alt eration of ionic strength to which the enzyme complex was exposed prod uced a change in the absorption of the complex at 230 nm. The presence of HPO42- ions prevented changes in the UV absorption spectrum of PDC induced by the variation in ionic strength. The K+ and Na+ ions alone had no effect on the UV spectrum of PDC, Upon increasing the ionic st rength to which the enzyme complex was exposed, dramatic changes in th e circular dichroism (CD) pattern were observed. At 0.04 M ionic stren gth PDC exhibited a CD spectrum with minima at 216, 218 and 222 nm and a cross-over point at 215 nm. At 0.15 M ionic strength the CD spectru m of PDC exhibited minima at 223, 226, 228 nm and a cross-over point a t 221 nm. The presence of HPO42- ions prevented alterations in the CD spectrum of PDC induced by variations in ionic strength, The K+ and Na f ions had no effect on the CD spectrum of PDC.