Conformational stability of ferricytochrome c near the heme in its complex with heparin in alkaline pH

The stability of the methionine 80 sulfur¯heme iron bond of ferricytochrome c (cyt c) in its complex with heparin has been studied by absorption spectroscopy in the alkaline pH region at temperatures of 20¯80°C and low ionic strength. According to spectral data, the midtransition temperature (T1/2) of the cleavage of the sulfur¯iron bond was 57.5± 0.5 and 52.5±0.5°C for cytochrome c and cytochrome c¯heparin complex, respectively, at neutral pH. The increasing in pH caused an expressive fall of cyt c transition temperature while the T1/2 for cyt c in its complex with heparin was constant and from pH>7.7, this value was higher than that for the free cyt c. Addition of heparin to cyt c evoked a moderate increase of 695 nm band intensity at neutral or slightly alkaline pH. It was shown that heparin stabilises the conformation of cyt c in state III (the Met 80 ¯heme iron bond is presented) in alkaline pH region and physiological temperature range.