Extraction of proteins from rubber particles by SDS solution, enzymatic deproteinization and saponification reaction
The large and small rubber particles obtained from centrifugation were dispersed in 2% (w/v) SDS and stirred overnight at 4°C. Each mixture was then centrifuged at 19,000 rpm for 1 h at 20°C to remove rubber particles from the aqueous phase which contained soluble proteins.
The 30% dry rubber content (DRC) of large rubber particles in 0.2% (w/v) Triton®X-100 solution was incubated with 0.04% (w/v) proteolytic enzyme (KP 3939) at 37°C for 16 h followed by centrifugation at 14,000 rpm for 1 h (11). The cream fraction was redispersed in 0.2% (w/v) Triton®X-100 solution and recentrifuged under the same conditions. The deproteinized natural rubber (DPNR) latex was obtained from the dispersion of the cream fraction in a 0.2% (w/v) Triton®X-100 aqueous solution.
To decompose phospholipids deproteinized natural rubber latex was treated with 1% (w/v) NaOH at 70°C for 3 h in a saponification reaction (18) and then centrifuged at 19,000 rpm for 1 h at 20°C to separate the serum fraction.
Proteins precipitation with TCA in acetone
The serum fraction was prepared in the presence of 10% (w/v) trichoroacetic acid (TCA) in acetone with 0.07% (v/v) 2-mercaptoethanol. Proteins were subjected to precipitate for 45 min at − 20°C. Pellet proteins were collected by centrifugation and were further washed with cold acetone containing 0.07% (v/v) 2-mercaptoethanol. Residual acetone was removed by air-drying and the proteins were redissolved in lysis buffer, 8 M urea, 4% (v/v) CHAP, 60 mM DTT and 2% (v/v) PharmalyteTM.