At least 23 different variants of Interferon- alpha are known. The individual proteins have molecular masses between 19-26 kD and consist of proteins with lengths of 156-166 and 172 amino acids. All IFN- alpha subtypes possess a common conserved sequence region between amino acid positions 115-151 while the amino-terminal ends are variable. Many IFN- alpha subtypes differ in their sequences at only one or two positions. Naturally occurring variants also include proteins truncated by 10 amino acids at the carboxyl-terminal end.
Lyophilized protein should be stored at -20˚C, though stable at room temperature for 3 weeks. Reconstituted protein solution can be stored at 4-7˚C for 2-7 days. Aliquots of reconstituted samples are stable at -20˚C for 3 months.