Malic acid is a tart-tasting organic dicarboxylic acid that plays a role in many sour or tart foods. Apples contain malic acid which contributes to the sourness of a green apple. Malic acid can make a wine taste tart although the amount decreases with increasing fruit ripeness.

3-Methylhistidine belongs to the class of organic compounds known as histidine and derivatives. Histidine and derivatives are compounds containing cysteine or a derivative thereof resulting from reaction of cysteine at the amino group or the carboxy group or from the replacement of any hydrogen of glycine by a heteroatom.

Vasopressin (argipressin), a cyclic nine-peptide synthesized by hypothalamic neurons, is one of the hormones involved in peptide prohormone synthesis.