Lactacystin is primarily used in biological research as a selective and potent inhibitor of the proteasome, a complex responsible for degrading damaged or unnecessary proteins in cells. By inhibiting proteasome activity, it helps scientists study the role of protein degradation in cellular processes, such as cell cycle regulation, apoptosis, and signal transduction. This compound is particularly valuable in cancer research, as it allows researchers to explore the effects of proteasome inhibition on tumor growth and survival. Additionally, lactacystin is used in neuroscience to investigate the role of protein aggregation in neurodegenerative diseases like Alzheimer's and Parkinson's. Its ability to induce apoptosis in certain cell types also makes it a useful tool for studying programmed cell death and its implications in various diseases.