Mono-Pegylated Leptin Rat Recombinant produced in E.Coli is a single, non-glycosylated, polypeptide chain containing 147 amino acids and an additional Ala at N-terminus having a molecular mass of 35.6 kDa (with 20 kDa PEG) as determined by mass spectometry. However due to enlarged hydrodymanic volume it runs on the SDS-PAGE as 48 kDa protein and in gel-filtration on Superdex 200 as over 100 kDa protein. Its half-life in circulation after SC injection was over 20 hours. Rat Leptin was purified by proprietary chromatographic techniques according to Salomon et al (2006) Protein Expression and Purification 47, 128-136 and then pegylated.. Purity >99.0% as determined by: (a) Analysis by Gel-Filtration. (b) Analysis by SDS-PAGE.