PKLR is a pyruvate kinase which catalyzes the trans phosphorylation of Phosphoenolpyruvate into pyruvate and ATP. That is the rate-limiting step of glycolysis. PKLR gene encodes the L- and R-type isoenzymes through alternate splicing events controlled by different promoters. The L-type isoform can also appear as a tetramer and is upregulated by glucose with implications in maturity-onset diabetes of the young.