Biosynthesis of Hordenine in Tissue Homogenates of Panicum miliaceum L.

He postulated that tyrosine (I) is decarboxylated to tyramine (II) which through a stepwise methylation forms N-methyltyramine (III) and subsequently hordenine (IV). Attempts to verify this postulated reaction sequence have been partially successful. Leete, Kirkwood and Marion (10) administered tyramine-2-C14 to sprouting barley and isolated radioactive hordenine and N-methyltyramine from the roots. The specific activity of the N-methyltyramine was about 10 times that of hordenine, and it was concluded that tyramine undergoes methylation in the barley root to form N-methyltyramine and then hordenine. Leete and Marion (11) then fed DL-tyrosine-2-C14 to sprouting barley and were able to isolate radioactive hordenine and N-methyltyramine from the roots of the plants. Degradation of these alkaloids showed that all of the activity was located in the 2-carbon of the side chain, indicating that tyrosine is a precursor of N-methyltyramine and hordenine. In a similar experiment Massicot and MIarion (12) isolated radioactive hordenine from barley roots after feeding phenylalanine-2-C14 and considered this evidence for the conversion of phenylalanine to tyrosine in that plant. L-Methionine labeled with C14 in the methyl group was fed to sprouting barley by Matchett, Marion and Kirkwood (13). Radioactive hordenine was isolated and degraded. This showed that all of the radioactivity in the molecule was in the N-methyl groups. It was concluded that methionine serves as an efficient methyl donor for hordenine biosynthesis in barley seedlings. In a recent work James and Butt (8) were able to verify in part the results of Marion et al. Tyramine and methionine were incubated with excised barley