PKOPEETIES OF AMINES 169 



Many of the biologically produced amines have physiological 

 or pharmacological activities, and so their production in vivo 

 by bacteria might have important consequences. For 

 example, histamine, produced by the decarboxylation of 

 histidine, is known as a " depressor substance" in that injec- 

 tion of small quantities into an animal results in a rapid fall 

 in blood pressure. It also produces contraction of smooth 

 muscle and causes a general condition in the animal analogous 

 to " shock." Tyramine, on the other hand, is a " pressor 

 substance" in that injection causes a rise of blood pressure. 

 Its general properties are the opposite of those of histamine, 

 and its action on injection is similar to that of adrenaline, 

 but much less active weight for weight. Since the action of 

 tyramine resembles that of adrenaline which is secreted by 

 sympathetic nerve endings, tyramine is said to be a " sympa- 

 theticomimetic " drug, while histamine is " parasympathetico- 

 mimetic." The other amines are less active and, in general, 

 the diamines such as putrescine and cadaverine (from ornithine 

 and lysine respectively) have weak parasympatheticomimetic 

 activities, while the mon-amines have weak sympathetico- 

 mimetic activities. The guanidine nucleus in agmatine, 

 produced by decarboxylation of arginine, confers an insulin- 

 like activity upon this amine but it is not possible to use it 

 as an insulin substitute as its repeated administration gives 

 rise to liver damage. The products of decarboxylation of the 

 dicarboxylic acids have no known pharmacological properties, 

 although j8-alanine is a growth factor for some micro-organisms 

 and forms part of the pantothenic acid molecule. 



The amino-acid decarboxylases are formed only when growth 

 takes place in an acid environment, and they have unusually 

 acid activity -^H optima varying from 2-5 for histidine decar- 

 boxylase {CI. welchii) to 5-5 for the ornithine decarboxylase 

 of CI. sejpticum. Six of the enzymes have been obtained in a 

 cell-free condition and five of them, the decarboxylases of 

 lysine, arginine, ornithine, tyrosine, and glutamic acid, have 

 pyridoxal phosphate as prosthetic group. The histidine 

 decarboxylase apparently does not require this prosthetic group. 



