We have characterized the biochemical properties of the testis and brain-specific 105-kDa protein which is cross-reacted with an anti-bovine HSP90 antibody. The protein was induced ingermcells byheat stress, resulting inaprotein which is one of the heat shock proteins [Kumagai, J., Fuk-uda, J., Kodama, H., Murata, M., Kawamura, K., Itoh, H. &Tanaka,T. (2000)Eur. , 3073–3078]. In the present study,we characterized thebiochemical propertiesof the protein.