Notice -ine is the ending for all amino acids. When it is removed the amino group becomes an ammonia molecule. The ability of a bacterium to deaminate phenyalanine is a common assay used in identification of intestinal bacteria. The -COOH group is the carboxyl group. The ability of a bacterium to remove the carboxyl group of arginine, lysine, and ornithine is an important assay in identification of intestinal bacteria.
Biochemists use the suffix -in to designate proteins.
Peptones are soluble pieces cut from proteins. Since gelatin is a fairly pure and cheap protein, it is useful for testing the abililty of bacteria to digest a particular protein. There are lots of proteins around the home that you can use use high protein media. Some of those used by professionals are meat, brain, egg, liver, gelatin, can add to TGY and other bases. Skim milk contains the disaccharide lactose and two protein complexes and is a useful medium covered on page b028 .