Graph theoretical analysis is an important area of the research in biological networks. Here first we introduce Pt-graph of peptide/protein based on physicochemical properties and adjacency of amino acids in the corresponding peptide/protein. Based on the Pt-graph, we introduce the graph of species which containing the peptide/protein named as SPt-graph. Finally, we analyze graph theoretically Pt-graphs of fourteen species of animals containing Galanin, a neuropeptide and their SPt-graph. From the graph theoretical analyses of Pt-graph and SPt-graph we get some observations about the relations among the amino acids, physicochemical properties of amino acids, peptide/protein and species containing peptide/protein and it may help in the field of evolution of peptide/protein and drug design in future
