ABSTRACT
According to the SCOP database, IN belongs to the class of small proteins, with an insulin-like fold, classified as disulfide rich and nearly all-a [14]. This fold classifica tion, besides other insulin-like proteins (relaxin, insulin-like growth factor, bombyxinII), includes IN from Bos taurus, Homo sapiens, and Sus scrofa. At present, 85 IN structures are available in the Protein Data Base, but in the present chapter only those concerning the zinc protein will be described and discussed (see the PDB refer ences in Table 2 ). The zinc-containing proteins have been isolated in different crystal line forms, called 2-zinc hexamer and 4-zinc hexamer (even if the zinc content is less than 3) and phenol-induced IN species [37-42].
