Isolation and identification of two [3H]norharman- ([3H]β-carboline)-binding proteins from rat liver

Norharman (9H-pyrido-[3,4-b]indol) represents a member of the mammalian alkaloids with the group name β-carbolines. In mammals, it exhibits psychotropic and co-mutagenic actions. Highly specific [3H]norharman binding sites have been detected in the liver of rats (Bmax: 11 pmol mg−1 protein; KD: lower nanomolar range). Two [3H]norharman binding proteins with apparent molecular masses of 60 and 80 kDa (SDS–PAGE) were isolated from rat liver crude membrane fraction and identified as the enzyme carboxylesterase (EC 3.1.1.1; 60 kDa) and the stress protein glucose-regulated protein 78 (GRP78; 78 kDa). Possible functional consequences of the interaction of norharman with these two proteins are discussed.