Alternative splicing of the pyruvate kinase M (PKM) pre-mRNA generates two isoforms, PKM1 and PKM2. PKM catalyzes the conversion of phosphoenol-pyruvate to pyruvate in glycolytic pathway. PKM1 exist as a stable tetramer that is at an active enzyme state, while PKM2 is in equilibrium among monomer, dimer and tetramer under the regulation of its allosteric activators. Many cancer cells show the feature of higher glucose uptake and lactate production in spite of oxygen availability, which is known as the Warburg effect. PKM2 is upregulated in most cancer types and the inactive PKM2 lead to the cancer metabolism. In addition, dimeric PKM2 induces its nuclear translocation through posttranslational modification and acts as a transcriptional co-activator for the expression of oncogenes. Therefore, it is important to elucidate mechanisms for modulation of an active or inactive state of PKM2, namely the tetramer-to-dimer-transition. The definitive difference between PKM1 and PKM2 is to constitutively form tetramer or not in the cytoplasm, which is ascribed to 22 amino acids derived from exon 9 (PKM1) or exon 10 (PKM2). In this study, we generated 22 different PKM1-mimetic point mutants of PKM2, and demonstrated that replacement of cysteine424 residue of PKM2 with leucine424 conserved in PKM1 (C424L) promote its tetramerization. PKM2(C424L) formed a tetramer without allosteric activator, and escaped the inhibitory effects by oxidative stress, like PKM1. Our findings intensely suggest that C424 or L424 determines the different catalytic and modulatory properties between PKM splicing isoforms. (C) 2020 Elsevier Inc. All rights reserved.