3.3 Characteristic size of biological macromolecules
Dissolving in 20 mM AmAc, serially-diluted samples were prepared and the correlation between the protein concentration and size distribution was investigated. At 10-1 mg/ml scale of the protein concentration in electrolyte, only the BSA exhibited clear and separate peaks among size distribution, as shown in Figure 3(A) . Based on the electrophoretic mobility of NP, the primary peak, the representative size, was 6.9 nm, and the dimer (8.8 nm), and trimer (10.2 nm) of BSA could be clearly recognized [17]. On the other hand, the ubiquitin, LDL, and HDL possessed wider range of size distribution and the positions of monomer, dimer, and etc., were obscure (Figure 3 (B) -(D) ). At the concentration of 10-3 mg/ml, the representative sizes of ubiquitin revealed and were 3.6 nm and the dimer was 4.6 nm for ubiquitin. Although a primary peak at 10.2 nm and 20.9 nm extinguished in HDL and LDL sample at 10-3 mg/ml protein concentration, the emergence of multiple peaks with inconsistent relation between size and number could not be explained by the theory of NP charging efficiency [20]. Consequently, HDL and LDL that possessed unknown electrophoretic behavior was not considered as the RM in this article.