Lactacystin, an antibiotic Streptomyces spp. metabolite, is a potent and selective proteasome inhibitor with an IC₅₀ of 4.8 μM for 20S proteasome. Lactacystin also inhibits the lysosomal enzyme cathepsin A^[1]. Lactacystin inhibits cell growth and induces neurite outgrowth^[2]. IC50 & Target: IC50: 4.8 μM (proteasome)^[1] In Vivo: Lactacystin (microinjection; 2 µg) induces a Parkinson’s disease-like motor phenotype 5-7 days after injection in young and adult mice^[2].