EPR studies on a Hipip type iron-sulfur center in the succinate dehydrogenase segment of the respiratory chain

Succinate Dehydrogenase

“…SA). The signal has a peak to trough width of 27 G and rapidly decreased in intensity as the temperature was raised above 12 to 15 K. The above properties coincide with those reported previously for center S-3 from both mammalian (20) and higher plant sources (23).…”

“…In isolated mammalian SDH, the EPR signal of center S-3 is extremely susceptible to breakdown in the presence of oxidants such as ferricyanide or even 02. Further, modification of center S-3, as indicated by the lack of the EPR signal, correlated with the inability of the SDH preparation to reconstitute succinateCyt c reductase activity when combined with either soluble Cyt bc, complex or alkaline-treated submitochondrial particles (20). No attempts at reconstitution were made in the current study, but given the lack of quinone reductase activity, it seems unlikely that the plant preparation would be active in reconstitution experiments even though the HiPIP-type EPR signal is present.…”

“…The two centers differ in their reduction potentials (S-1 is succinate reducible, S-2 requires dithionite) and in their apparent relaxation rates (21). Center S-3 produces a relatively symmetric EPR signal centered around g = 2.01 with a peak to trough width of about 25 G (20). EPR signals associated with all three iron-sulfur centers found in mammalian SDH have been reported in plant mitochondria (22,23).…”

“…In mammalian SDH, iron-sulfur centers S-1 and S-2 both give ferredoxin-type EPR signals in their reduced state (21), whereas center S-3 produces a HiPIP-type EPR signal when oxidized (20). The EPR signals from centers S-1 and S-2 both show rhombic symmetry and have very similar g-values (gz = 2.03, gy = 1.93, gx = 1.91).…”

“…The 70,000 D polypeptide contains two iron-sulfur centers of the Fe2S2 type, named centers S-1 and S-2, and has 1 mol of covalently bound flavin adenine dinucleotide (4,21). The 27,000 D polypeptide contains a Fe4S4 center referred to as iron-sulfur center S-3 (20). Complex II contains two additional polypeptides with mol wt of 15,000 (Cyt b5m) and 13,000 D (possibly a ubiquinone-binding protein) (1,29).…”