Amino-acids 185 



AMINO-ACIDS 



The concentrations of free amino-acids in human saliva have 

 been measured by microbiological assay and by paper and column 

 chromatography (Kirch, Kesel, O'Donnell and Wach, 1947, 1953; 

 Berry, 1951; Moor and Gilligan, 1951 ; Berry and Cain, 1951 ; 

 Capozzi, 1954; Woldring, 1955; Rose and Kerr, 1958). Free 

 amino-acids are present in saliva although in concentrations lower 

 than in plasma. For the most part the concentrations are of the 

 order of 10-20 per cent of the plasma level, but higher percentages 

 have been reported for glycine, histidine, isoleucine and tyrosine. 

 In addition, quite large amounts of y-amino glutamate, taurine 

 and O-phosphoethanolamine are found in both parotid and sub- 

 maxillary salivas and indeed represent the most intense ninhydrin- 

 positive spots on the paper chromatogram. In submaxillary saliva 

 part of the O-phosphoethanolamine appears as the hydrolytic 

 product ethanolamine due to the action of the weak alkaline phos- 

 phatase present in the saliva. When the level of free amino-acids 

 in the blood is raised, the concentrations in the saliva follow the 

 plasma levels passively. Rose and Kerr found no appreciable 

 change in the saliva amino-acid pattern in patients with cystinuria 

 and hypophosphatasia. They also found that the concentration of 

 amino-acids was lower when the salivary flow rate was high than 

 when it was low. Martin (1959) has found that with the exception 

 of proline and hydroxyproline which are present in saliva at about 

 half the plasma concentration, all the other amino-acids in dog 

 parotid saliva are present at less than 10 per cent of the plasma 

 level. Phosphoethanolamine, taurine and y-amino glutamate are 

 not present in appreciable amounts in dog saliva. Rather higher 

 concentrations of all the amino-acids were found in dog submaxil- 

 lary saliva. Intra-arterial injection of C 14 -valine, tyrosine, methio- 

 nine or isoleucine into the arterial supply to the parotid gland did 

 not lead to the appearance of detectable amounts of either free or 

 protein-bound labelled amino-acids in the saliva within two min- 

 utes of injection. This means either that a relatively large amino- 

 acid pool exists in the salivary gland to supply immediate needs 

 for protein synthesis or that the amino-acid is effectively trapped 

 by a peptide synthesis within the gland with delayed release of 

 the protein. Amberson and Hober (1932) found the perfused cat 

 submaxillary gland to be impermeable to glycine and alanine. 



