The alpha 1 and alpha 2 isoforms of the AMP-activated protein kinase have similar activities in rat liver but exhibit differences in substrate specificity in vitro

The AMP-activated protein kinase (AMPK) is a heterotrimeric complex composed of a catalytic subunit (alpha) and two regulatory subunits (beta and gamma). Two isoforms of the catalytic subunit (alpha 1 and alpha 2) have been identified, We show here that the alpha 1- and alpha 2-containing complexes contribute approximately equally to total AMPK activity in rat liver, Furthermore, expression of alpha 1 or alpha 2 with beta and gamma in mammalian cells demonstrates that both complexes have equal specific activity measured with the SAMS peptide, Using variant peptides, however, we show that alpha 1 and alpha 2 exhibit slightly different substrate preferences, which suggest that the tao isoforms could play different physiological roles within the cell.