Plant peptide-based toxins

Hundreds of applications have been mentioned in the Zweig (1968) review acids, alkaloids, amino acids, antibiotics, antioxidants, food and feed additives, bases and amines, bile acids, carbonyls, dyes, enzymes, lipids, hydrocarbons, hormones, indoles, natural products, peptides, proteins, pesticides, plant growth regulators, pharmaceutical products, phenols, pigments (chlorophylls, xanthophylls, porphyrins, melanin, pterins, pteridines, anthocyanins, ilavonoids, etc.), polymers, purine and pyrimidine derivatives, quinones, RNA, DNA, organic sulfur compounds, steroids, sugars, toxins, vitamins, inorganic ions, and others. 

In general, nonconventional protein foods must be competitive with conventional plant and animal protein sources on the bases of cost delivered to the consumer, nutritional value to humans or animals, functional value in foods, sensory quality, and social and cultural acceptability. Also, requirements of regulatory agencies in different countries for freedom from toxins or toxic residues in single-cell protein products, toxic glycosides in leaf protein products, pathogenic microorganisms, heavy metals and toxins in fish protein concentrates, or inhibitory or toxic peptide components in synthetic peptides must be met before new nonconventional food or feed protein products can be marketed. 

Another example of the use of mass spectrometry to delect toxins is to identify ricin, a highly toxic protein that inhibits cell protein synthesis. Ricin is produced from the seeds of Ricinus communis plants (known conunonly as castor beans) [73]. Structurally, ricin is made of A- and B-chains linked by a disulfide bridge. The toxicity of ricin is due primarily to the A-chain, which acts as an RNA A-glycosidase, which leads to ribosome incapacitation and ultimately to cell death. Ricin was identified from crude castor bean extracts using LC-MS/MS. The extract was denatured, reduced, and alkylated prior to trypsin digestion. Ricin identification was based on the detection of marker peptides in the digest. These markers include T5, T7, Til, T12, and T13 from the A-chain and T3, T5, T14, T19, and T20 from the B-chain. MS/MS can provide the amount and sequence of each marker for irrefutable evidence. For quick screening of ricin in crude extracts, MALDI-MS can be used to provide the molecular mass profile of the marker peptides. 

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