The HSP90α (C-Terminal Domain) TR-FRET assay kit is designed to measure the inhibition of HSP90α binding to its protein target PPID (also known as Cyclophilin D or Cyp40) in a homogeneous, 384 reaction format. This assay requires no time-consuming washing steps, making it especially suitable for high throughput screening applications. The assay procedure is straightforward and simple. A sample containing terbium-labeled donor, dye-labeled acceptor, HSP90α, substrate, and an inhibitor is incubated for 2 hours. The protein-protein interaction is then assayed by measuring the TR-FRET between the PPID and HSP90α using a fluorescence reader.