The PKLR gene codes for pyruvate kinase, a key rate controlling glycolytic enzyme that catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate.
The two isoforms of the PKLR protein are coded for by the same gene, but by using different promoters. Therefore, the R-isozyme has an additional 33 amino acids. The remaining 541 amino acids are the same in both the forms.