C. Aliquots of the supernatants of the indicated HEK293T transfectants (all expressing λ chains) were resolved under non-reducing conditions and blotted with anti-µ antibodies. Wild type µs chains are secreted only as pentamers and hexamers, whilst mutants lacking C575 release mostly µs2L2 subunits (indicated with a red arrow) as does the double C414A-C575A. L566A releases instead mainly µs2L2 subunits of faster migration (blue arrow). C414 mutants release no hexamers, but smaller assemblies, including fast migrating µs2L2 subunits. 