Examples of zwitterions include amino acids, many metabolites, peptides, and proteins. Protease inhibitors can be other proteins, small peptides, or molecules. Prepropeptides often produce multiple copies of the same peptide or many different peptides. The hydrolysis of peptides gives amino acids. The toxins are composed of peptides and proteins. ECEPP was developed specifically for modeling of peptides and proteins. In this assay, the copper(II) binds with nitrogens present in the peptides of proteins. A number of algorithms for estimating isoelectric points of peptides and proteins have been developed. Dividing them into amino acids, peptides, and monoamines is sufficient for some classification purposes. Even larger cathelicidin peptides (39-80 amino acid residues) are also present. Polyphosphoinositide binding peptides for intracellular drug delivery. Autoantibodies in rheumatoid arthritis recognizing an epitope of citrullinated peptides are cross-reactive with filaggrin. They are part of a broader class of molecules called nonribosomal peptides. Exactly how causes the release of endogenous opioid peptides remains uncertain. A 2005 study in humans found hydrolyzed collagen absorbed as small peptides in the blood.