DCP MIDSTREAM, LLC, as Issuer and THE BANK OF NEW YORK MELLON TRUST COMPANY, N.A., as Trustee FIRST SUPPLEMENTAL INDENTURE Dated as of May 21, 2013 to Indenture dated as of May 21, 2013 5.85% FIXED-TO-FLOATING RATE JUNIOR SUBORDINATED NOTES DUE 2043