Conformational analysis of Na,K-ATPase in drug–protein complexes

Abstract This review reports the effects of several drugs such as AZT (anti-AIDS), cis -Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and conformation of Na,K-ATPase in vitro. Drug–enzyme binding was found to be via H-bonding to the polypeptide C O and C–N groups with two binding constants K 1(AZT)  = 5.30 (±2.1) × 10 5  M −1 and K 2(AZT)  = 9.80 (±2.9) × 10 3  M −1 for AZT and one binding constant K cis -Pt  = 1.93 (±1.2) × 10 4  M −1 for cis -Pt, K aspirin  = 6.45 (±2.5) × 10 3  M −1 and K ascorbate  = 1.04 (±0.5) × 10 4  M −1 for aspirin and ascorbic acid. The enzyme secondary structure was altered with major increase of α-helix from 19.9% (free protein) to 22–26% and reduction of β-sheet from 25.6% (free protein) to 17–23% upon drug complexation indicating a partial stabilization of protein conformation. The order of induced stability is AZT> cis -Pt > ascorbate > aspirin.