The behavior of holo- and apo-forms of bovine superoxide dismutase at low pH.
1. Holo-superoxide dismutase from bovine erythrocytes has been shown to undergo a reversible structural modification in the pH 3-5 range. 2. The spectral alterations observed on changing from neutrality to pH 2 were: a slight attenuation of the 680 nm absorbance; the loss of the 450 nm shoulder, apparent in the optical spectrum of the native protein; and a new band appeared at 330 nm. The circular dichroism at 600 nm was essentially lost while a weak negative band appeared at approx. 380 nm and a positive band at 310 nm. 3. The EPR spectrum was also modified on changing from the native to the low pH form: A parallel increased from approximately 130 to approximately 150 G, g parallel remained unchanged at approximately 2.27, and gm decreased from approximately 2.09 to approximately 2.08. The apparent linewidth remained essentially constant. 4. High resolution (220 MHz) PMR spectra of holo- and apoproteins revealed that the metals influence the three-dimensional structure of the protein. 5. PMR studies indicated that at pH 3 the apoprotein existed almost entirely in a random coil form and that it assumed a compact well-ordered structure on returning to neutral pH. The holoprotein maintained a compact, apparently dimeric, structure even at pH 3.
D000818:Animals; D001051:Apoenzymes / Q000097:blood; D001059:Apoproteins; D001665:Binding Sites; D002417:Cattle; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011485:Protein Binding; D011487:Protein Conformation; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013482:Superoxide Dismutase / Q000097:blood
D001051:Apoenzymes; D001059:Apoproteins; D013482:Superoxide Dismutase