Like all other organisms, parasitic  protozoa and helminths require the basic set of 20 amino acids for their protein synthesis, for the formation of other biomolecules and, to a lesser extent, for energy production. The majority of these amino acids are essential for the parasite and have to be obtained from their diet or from exogenous proteins. Ingested proteins are hydrolyzed within specialized organelles ( lysosomes, lysosome-like organelles and other specialized  vacuoles) into their constituent amino acids by the concerted action of specific  proteinases and  peptidases.The amino acid metabolism of parasites resembles that of higher animals, but there are differences regarding the properties of the enzymes involved, the relative importance of the various pathways and the occurrence of a variety of unusual metabolic routes. Like their hosts, parasites have the capacity to synthesize certain amino acids from simple carbon precursors by pathways that are also present in...