To predict the kinase substrate relationships from the dataset, the computer algorithm SCANSITE was used. SCANSITE makes use of peptide library phosphorylation data to predict substrates recognized by specific kinases. Tables S4 & S5 show the results of phosphopeptides that were identified in this study and were predicted to be associated with a kinase binding motif by SCANSITE at the different stringency levels. It was found that most of the phosphorylation sites determined in this study were phosphorylated by acidophilic serine/threonine kinase and proline-dependent serine/threonine kinase. Notably, we found fifteen sites that can be phosphorylated by the Casein Kinase 2 (CK2). CK2 is a constitutively active protein kinase implicated in cellular transformation and the development of tumorigenesis [23] . Aberrantly active in MM cells, CK2 controls the cell survival [24] . Our SCANSITE analysis suggests that CK2 may play an important role in bortezomib-induced apoptosis and may represent a potential target in MM therapy.