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Isolation of decay-accelerating factor (DAF) from rabbit erythrocyte membranes
1Department of Biochemistry, School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.
Abstract:
A regulatory protein purified from rabbit erythrocyte stroma had decay-accelerating activity to C5 convertases on hemolytic intermediate cells (EAC1-3b, P). Its molecular weight was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under non-reducing conditions to be 66,000, slightly smaller than that of human decay-accelerating factor (DAF). The amino acid composition of the protein resembled that of human DAF. The protein was incorporated into sheep erythrocytes. The incorporation and the decay-accelerating activity were inhibited by low density lipoprotein. It did not bind to rabbit C3-Sepharose in a column under conditions in which human CR1 bound, but its interaction with rabbit C3 was evident from the retardation of its elution from the column. These results indicate that the protein purified from rabbit erythrocyte stroma was DAF.
Insights
Researchers identified a decay-accelerating factor (DAF) in rabbit erythrocytes. This protein regulates complement activity and shares similarities with human DAF, despite some differences in binding.
Area of Science:
- Immunology
- Complement System Biology
- Erythrocyte Research
Background:
- The complement system is crucial for innate immunity.
- Regulatory proteins on cell surfaces prevent complement-mediated damage.
- Rabbit erythrocyte stroma contains proteins that may modulate complement activity.
Purpose of the Study:
- To purify and characterize a regulatory protein from rabbit erythrocyte stroma.
- To determine if this protein possesses decay-accelerating activity.
- To compare its properties to human decay-accelerating factor (DAF).
Main Methods:
- Purification of a regulatory protein from rabbit erythrocyte stroma.
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for molecular weight estimation.
- Assay of decay-accelerating activity on hemolytic intermediate cells.
- Amino acid composition analysis.
- Incorporation studies into sheep erythrocytes.
- Inhibition studies using low-density lipoprotein.
- C3-Sepharose chromatography to assess C3 binding.
Main Results:
- A protein with decay-accelerating activity on C5 convertases was isolated.
- The protein's molecular weight was estimated at 66,000 Da.
- Amino acid composition resembled human DAF.
- The protein incorporated into sheep erythrocytes and exhibited inhibitory effects from low-density lipoprotein.
- While not binding strongly to C3-Sepharose like human CR1, its interaction with rabbit C3 was confirmed by elution retardation.
Conclusions:
- The purified rabbit erythrocyte protein functions as decay-accelerating factor (DAF).
- It shares functional and compositional similarities with human DAF.
- Differences in C3 binding suggest potential species-specific interactions within the complement cascade.