Described are an oligopeptide sequence of any of RDHLVGRWIR (E1), IRRFKSSKFGCR (E2), RHLEIIYAINQR (E3). LIIKLVT (E4), WGDRLKVIF (E5), any combination of E1 to E3; or combination of E4 and E5. Further described is a detecting agent for specific detecting glycogen phosphorylase iso-enzyme BB (GPBB), wherein the detecting agent is characterized by specific recognizing and binding to (1) an epitope of the GPBB comprising an oligo-peptide sequence of any of RDHLVGRWIR (E1), IRRFKSSKFGCR (E2), RHLEIIYAINQR (E3) or any combination of E1 to E3; or (2)an epitope of GPBB comprising an oiigo-peptide sequence of LIIKLVT (E4), and/or WGDRLKVIF (E5), or combination of E4 and E5.