Catalyzes the dephosphorylation and concomitant reactivation of the alpha subunit of the E1 component of the pyruvate dehydrogenase complex. H2O + O-phospho-L-seryl-[pyruvate dehydrogenase E1 alpha subunit] = L-seryl-[pyruvate dehydrogenase E1 alpha subunit] + phosphate Binds 2 magnesium ions per subunit. Heterodimer of a catalytic (PDP1) and a regulatory (PDPR) subunit. The disease is caused by variants affecting the gene represented in this entry. Belongs to the PP2C family.