[pThr3]-CDK5 Substrate is an effective Phospho-Thr3CDK5 Substrate. [pThr3]-CDK5 Substrate is derived from the sequence of the histone H1 peptide that docks in the active site of CDK5. [pThr3]-CDK5 Substrate is phosphorylated by CDK5 with a K m value of 6 µM.