This thesis includes two parts. Part I, ‘Development of a peptide microarray method to study post-translational modifications’ and part II, ‘Toxicity of galectin-9 toward KRAS mutated CRC cells: pathway elucidation’. Part I aimed to study the posttranslational modifications (PTMs), O-GlcNAcylation/ de- O-GlcNAcylation, phosphorylation/ dephosphorylation, crosstalk between de-O-GlcNAcylation and dephosphorylation and finally O-GlcNAcylation of JAK2 JH1 kinase using short peptide substrates derived from their parental proteins. Part II of this thesis, ‘Toxicity of galectin-9 toward KRAS mutated CRC cells: pathway elucidation’, aimed to profile the STK and PTK activity of galectin-9 sensitive DLD-1 cancer cells using peptide microarrays. The goal was to identify the kinase pathways which are involved upon galectin-9 treatment and includes two chapters.