This book describes the lifelong research experience of a scientist, from the beginning studies of protein chemistry to the development of a protein drug. Also discussed herein include the invention of the first polymer conjugate drug¡ªpoly(styrene-co-maleic acid (SMA) conjugated to NCS, £­called SMANCS. The author, having acquired knowledge of proteases and inhibitors, pioneered investigations of microbial proteases in the pathogenesis of bacterial infection. The author¡¯s group, using a polymer-conjugated enzyme, discovered an enormous burst in the generation of superoxide anion radical during influenza virus infection by the generation of xanthine oxidase, which was found to be the major cause of the pathogenesis of this viral infection, which progressed even after the virus was eradiated.