Abstract: Sacccharomyces cerevisiae cells lacking the cytochrome c oxidase (CcO) assembly factor Coa2 are impaired in Cox1 maturation and exhibit a rapid degradation of newly synthesized Cox1. The respiratory deficiency of coa2Delta cells is suppressed by either the presence of a mutant allele of the Cox10 farnesyl transferase involved in heme a biosynthesis or through impaired proteolysis through the disruption of the mitochondrial Oma1 protease. Cox10 with a N196K substitution functions as a robust gain-of-function suppressor of the respiratory deficiency of coa2Delta cells, but lacks suppressor activity for two other CcO assembly mutant strains, coa1Delta and shy1Delta. The suppressor activity of N196K mutant Cox10 is dependent on its catalytic function and the presence of Cox15, the second enzyme involved in heme a biosynthesis. Varying the substitution at Asn196 reveals a correlation between the suppressor activity and the stabilization of the high mass homo-oligomeric Cox10 complex. We postulate that the mutant Cox10 complex has enhanced efficiency in the addition of heme a to Cox1. Coa2 appears to impart stability to the oligomeric wild-type Cox10 complex involved in Cox1 hemylation.