Abstract
Measurements were made at 20°C of the magnetic susceptibility of soluble succinate dehydrogenase (succinate: (acceptor) oxidoreductase, EC 1.3.99.1) (4 Fe/flavin) from beef heart. The resting enzyme and enzyme in the presence of fumarate or oxaloacetate appeared to be nearly diamagnetic. The addition of succinate, malonate, or malonate
plus succinate, and other treatments resulted in an increase in paramagnetism:
Δ
χM,Fe
= 1200×10
−6
c.
g.
s units (average) per penzyme iron atom. An excess of dithionite caused a larger increase in paramagnetism:
Δ
χM,Fe
= 2500×10
−6
c.
g.
s. units (average). The change due to dithionite was partially reversible upon autoxidation. We cannot account quantitatively for these changes in terms of the paramagnetic species observable by electron spin resonance.