How did South Carolina v katzenbach and Shelby v holder affect the voting rights act of 1965

In South Carolina v. Katzenbach (and similarly and much more recently, in 2013, in Shelby County v. Holder) South Carolina filed a complaint with the Supreme Court challenging the Voting Rights Act as unconstitutionalon respect to state's rights. Many outhern states follow suit. This provoked the Supreme Court to pass judgement before the elections of 1966, upholding the Voting Rights Act and thus enabling almost a million of African Americans to register to vote.