The primary structure of snake (Zaocys dhumnades dhumnades, Cantor) insulin.

Snake insulin is isolated and crystallized from the pancreas of non-venomous snake (Zaocys dhumnades dhumnades, Cantor). The crystalline form is not rhombohedral but dodecahedral. The primary structure has been determined with the aid of an LKB solid-phase sequencer. In the primary structure of snake insulin, the presence of B5 Arg, B29 Arg, B16 Phe, B25 Tyr and B18 Ile is unusual in comparison with insulins from mammals, birds and fishes. However, the snake insulin we studied is very similar to rattle snake insulin, with the exception that A15 is glutamic acid instead of glutamine and B30 is threonine instead of serine. These differences are consistent with the higher acidity of the snake insulin we studied and with the threonine and serine content in amino acid analysis. The B10 residue of the snake insulin we studied is still histidine. The formation of dodecahedral crystals of the snake insulin has been discussed in connection with the presence of this histidine.