Some Typical Results

In the following sections we emphasize the conclusions that can be drawn from our studies.

Free Radical Formation

As a result of the reaction of COOradical with the protein, disulfide free radicals are created. Their absorption spectrum is made of a broad band with no structure, centered at about 420-440 nm (Fig. 2).

In acidic medium, the spectrum is shifted to the UV, indicating the formation of the protonated disulfide radical. The maximum is at about 400 nm and the extinction coefficients are lower.

Under the conditions described above, formation of the free radical is over in — 10-250 /¿sec. The rate constants of disulfide radical formation [reaction (1) of

fig. 2. Absorption spectra of disulfide anion (♦) and protonated (•) immunoglobulin G (IgG). These spectra were taken at the time when the absorbances were maximum. [IgG], 250 /iM: [HCOO-], 0.1 M; phosphate, 10 mM; N2O atmosphere; dose, ~25 Gy.

Wavelength (nm)

fig. 2. Absorption spectra of disulfide anion (♦) and protonated (•) immunoglobulin G (IgG). These spectra were taken at the time when the absorbances were maximum. [IgG], 250 /iM: [HCOO-], 0.1 M; phosphate, 10 mM; N2O atmosphere; dose, ~25 Gy.

4000 m X

o"

2500 35 n

0 0

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