Table 1.

Chemical features of FMS₇–IFN-α2

Characteristic	Numerical value
Moles FMS/mol IFN-α2*	7.0  ± 0.2
Absorbance at 280 nm†	ɛ280 = 166,500
Absorbance at 301 nm‡	ɛ301 = 76,200
Mass spectra§
Calculated	21,383 daltons
Found	21,382 daltons
Solubility in aqueous buffer, pH 7.4	>0.5 mg/ml
Retention time (analytical HPLC)¶	37.80 min
Reversion (%) to native IFN-α2 upon incubation at pH 8.5, 37°C, for the following durations (h)‖
4	3
9	10
20	30
50	97

^*Determined by UV spectroscopy, measuring the absorbance at 280 and 301 nm. Derivative concentration was determined by acid hydrolysis of a 20-μl aliquot, followed by amino acid analysis; calculated according to aspartic acid (14 residues), alanine (9 residues), and isoleucine (8 residues). 

^† Native IFN-α2 absorbs at 280 nm with ɛ₂₈₀ = 18,070 (18). 

^‡ Native IFN-α2 absorbs at 301 nm with ɛ₃₀₁ = 4,100. 

^§ Mass spectra were determined by using the electrospray ionization technique. 

^¶ IFN-α2 elutes under identical analytic HPLC procedure with retention time = 34 ± 0.2 min. 

^‖ Determined by analytical HPLC procedure (increase in peak area corresponding to native IFN-α2).