The present invention is related to a novel protein p140 polypeptide which is a key protein involved in the signal transmission system of insulin; method for preparation of it; DNA encoding the said polypeptide; vector derived the said DNA; host cells transformed the said vector; antibody of the said polypeptide; pharmaceutical composition containing the said peptide or antibody; method for the prevention and/or treatment of diabetes, which is characterized by tyrosine phosphorylation of the said protein p140; agent for the prevention and/or treatment of diabetes, agent for the prevention and/or treatment of diabetes, which is characterized by containing a compound which can tyrosine phosphorylate of protein p140, as active ingredient and the screening methods of the said prevention and/or treatment agent. Tyrosine phosphorylation of protein p140 is an essential step in the induction of hypoglycemia by glucose uptake. Method and agent of prevention and/or treatment based on tyrosine phosphorylation of protein p140 in the present invention is not only to improve the diabetes-derived hypoglycemic conditions but are also useful for the treatment and/or prevention of diabetes, especially non-insulin dependent diabetes mellitus (NIDDM).