Isolation of antibacterial peptides with low molecular weight from the spleen of Anguilla japonica

The acetic acid extract of the spleen from Japanese eel,Anguilla japonica,was separated by tangential flow ultrafiltration with 10 and 3 ku fibre columns,and the two protein samples of the molecular weight(Mw)10 ku and the Mw3 ku were purified by using the cationic exchange liquid chromatography together with reverse-phase high-performance liquid chromatography(RP-HPLC).The results showed that three compositions(the protein samples of Mw10 ku,Mw10 ku and Mw3 ku)were separated from the acid extract with two fibre columns.The samples of Mw10 ku and Mw3 ku exhibited stronger antibacterial activity than the protein sample of the Mw10 ku.The protein sample with the Mw10 ku was purified by the cationic exchange liquid chromatography and using pH 9 buffer solution in RP-HPLC,and we obtained an antibacterial peptide with the molecular weight of 1 391.82 u when determined by MALDI-TOF MS.The pH 9 and the pH 2 buffer solutions were applied in RP-HPLC of the factions obtained from cationic exchange liquid chromatography of the protein sample with the Mw3 ku,and we also obtained an antibacterial peptide with the molecular weight of 839.19 u when determined by MALDI-TOF MS.This study suggests that the main antibacterial components in the spleen of A.japonica are the proteins of low molecular weight.