Catalyzes the ATP-dependent amidation of the two carboxylate groups at positions a and c of cobyrinate, using either L-glutamine or ammonia as the nitrogen source. Is able to use other nucleotide triphosphates as substrate, such as GTP or UTP, although less efficiently than ATP. 2 ATP + cob(II)yrinate + 2 H2O + 2 L-glutamine = 2 ADP + cob(II)yrinate a,c diamide + 2 H(+) + 2 L-glutamate + 2 phosphate kcat is 0.16 sec(-1). The catalytic activity is essentially constant between pH 6.8 and 8.0. Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from sirohydrochlorin (anaerobic route): step 10/10. Monomer. Comprises of two domains. The C-terminal domain contains the binding site for glutamine and catalyzes the hydrolysis of this substrate to glutamate and ammonia. The N-terminal domain is anticipated to bind ATP and cobyrinate and catalyzes the ultimate synthesis of the diamide product. The ammonia produced via the glutaminase domain is probably translocated to the adjacent domain via a molecular tunnel, where it reacts with an activated intermediate. The a and c carboxylates of cobyrinate are activated for nucleophilic attack via formation of a phosphorylated intermediate by ATP. CbiA catalyzes first the amidation of the c-carboxylate, and then that of the a-carboxylate. Belongs to the CobB/CbiA family.