Quick Definition
What is BSA (Bovine Serum Albumin)?: Bovine serum albumin (BSA) is the most abundant protein in bovine blood serum (~60% of total protein), extracted from bovine plasma and purified to >96% purity. It is the most widely used protein supplement in biochemistry — used as a blocking agent in ELISA, as a carrier protein in serum-free medium, as an enzyme stabiliser, and as a drug binding protein in DMPK assays.
BSA grades — which one do you need?
Standard BSA: ELISA blocking, western blot blocking, antibody diluent, general protein standard — most cost-effective for high-volume non-critical applications.
BSA Low Endotoxin (<1 EU/mg): Cell-based assays, cytokine assays, receptor binding studies — standard BSA contains 1–100 EU/mg endotoxin from Gram-negative contamination during processing.
BSA Fatty Acid Free (FAF): PPAR and nuclear receptor assays, IVF fertilisation medium, DMPK microsomal protein binding correction (fu,mic) — fatty acids in standard BSA activate receptors non-specifically.
BSA vs rHSA
BSA for non-human cell lines, general blocking, and DMPK fu,mic correction. rHSA for xeno-free ATMP manufacturing, human-relevant DMPK fu,plasma measurements, and GMP cell culture.
Key Facts
- Most abundant protein in bovine serum, MW ~66.5 kDa
- Primary functions: fatty acid carrier, drug binding (Site I warfarin, Site II diazepam), ROS scavenger, osmotic pressure
- Used in ELISA blocking at 1–5% BSA/PBS — saturates non-specific protein binding sites on plastic surfaces
- Used in serum-free cell culture at 1–5 mg/mL to replace albumin function of FBS
- Three key grades: Standard (>96% purity), Low Endotoxin (<1 EU/mg), Fatty Acid Free (FAF)
- Drug binding: BSA binds differently than HSA for many drugs — use rHSA for human-relevant protein binding assays in DMPK
Further Reading
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