... dilution of known amounts of recombinantS proteins was used to plot a standard curve. The amount of HBsAg present in serum was determined according to the amount of recombinant S protein. The result ... proteinscontain the surface antigen (S) (226 amino acids), whilean N-terminal extension of S by 55 amino acids (desig-nated as preS2) results in the M protein (281 aminoacids). The L protein ... Gu1, Ming Luo1,3 and Xiaofeng Zheng*1,2Address: 1National Laboratory of Protein Engineering and Plant Genetic Engineering, Peking University, Beijing, 100871, China, 2Department of Biochemistry...