Yeast ornithine

M. J. C. 1990. Over-expressing a yeast ornithine decarboxylase gene in transgenic roots of Nicotiana rustica can lead to enhanced nicotine formation. Plant Molecular Biology, 15 111-114. 

HAMILL, J.D., ROBINS, R.J., PARR, A.J., EVANS, D.M., FURZE, J.M., RHODES, M.J.C., Over-expression of a yeast ornithine decarboxylase gene in transgenic roots of Nicotiana rustica can leads to enhanced nicotine accumulation. Plant Mol. Biol, 1990,15, 27-38. 

Hamill JD, Robins RJ, Rhodes MJC (1989) Alkaloid production by transformed root cultures of Cinchona ledgeriana. Planta Med 55 354-357 Hamill JD, Robins RJ, Parr AJ, Evans DM, Furze JM, Rhodes MJC (1990) Overexpressing a yeast ornithine decarboxylase gene in transgenic roots of Nicotiana rustica can lead tq enhanced nicotine accumulation. Plant Mol Biol 15 27-38 Hamill JD, Rounsley S, Spencer A, Todd G, Rhodes MJC (1991) The use of the polymerase chain reaction in plant transformation studies. Plant Cell Rep 10 221-224 Hartmann T, Toppel G (1987) Senecionine N-oxide, the primary product of pyrrolizidine alkaloid biosynthesis in root cultures of Senecio vulgaris. Phytochemistry 26 1639-1643... 

The free amino acids in bakers yeast were determined, ornithine (318) ranking third and proline (89 mg per 100 g) 11th. None of the amino acids ranked above proline, other than ornithine, was an effective precursor for ACPY or ACTPY. 

Proline is a particular case in the Maillard reaction because it is, unlike other amino acids, a secondary amine. It represents an important precursor for popcom-like aroma compounds in the reaction with reducing sugars such as glucose [46]. The relevant aroma compounds in this reaction are 2-acetyl-l-pyrroline (22), l-(l,4,5,6-tetrahydro-2-pyridyl)-l-ethanone (23) and its isomer l-(3,4,5,6-tetrahydro-2-pyridyl)-l-ethanone (24) [47], The formation pathway (Fig. 3.25) shows the important intermediates 2-oxopropanal (7) and 1-pyrroline (25) [48, 49[. Another amino acid precursor for 22 is ornithine, an amino acid in yeast or yeast extracts [49[. 

Ornithine decarboxylase and polyamine M. racemosus Initial 30-50-fold increase in activity of ODC throughout yeast to hyphal transition 123... 

The amino acid composition of the must also affects the formation of H2S by yeast. Besides cysteine and homocysteine, the following amino acids promote the production of H2S aspartic and glutamic acids, glycine, histidine, homoserine, lysine, ornithine, threonine and serine. Methionine prevents the formation of H2S by retroinhibiting the activation channel and reducing sulfates. 

C6H9NO, Mr 111.14. Rusty liquid with popcom-like odor, bp. 26-28 °C (10 Pa) rapid darkening of color at 20 °C, limited storage life at-20°C, 1% in pentane olfactory threshold in water 0.1 ppb. TVpical bread and rice flavor. A. is formed from yeast constituents on heating L- ornithine and 2-oxopropanal. The bread aroma 2-acetyl-A A )-tetrahydropyridine [C7H,NO, Mr 125.17,bp. 33-34 °C(0.12 kPa), olfactory threshold 1.6 ppb] is formed analogously from l- proline and 2-oxopropanal. 

Pi rard et al. (43) have demonstrated that the synthesis of carbamyl phosphate synthetase II in E. coli is under repressor control and that a single species of this enzyme serves both the arginine and pyrimidine pathways. Uridylate is a negative effector of the synthetase and ornithine reverses this inhibition (44)- The existence of two separate Type II synthetases has been demonstrated in yeast, one each serving the arginine and pyrimidine pathways (45). 

Ornithine Biosynthesis. Two reaction sequences leading to ornithine synthesis from glutamic acid have been described. In Neurospora and the yeast Tondopsis utilis the sequence involves the simple transamination of glutamic semialdehyde (IV). The reaction proceeds much... 

In the baking of white bread, ornithine comes from yeast where it is found in a concentration about four times that of free proline. 

A common basic amino acid is the lower homologue of lysine, L-ornithine (L-2,5-diaminovaleric acid, 2-41), which is an intermediate in the biosynthesis of arginine and an important amino acid of the ornithine (urea) cycle, which has the function of converting toxic ammonia into less toxic urea in mammals. Ornithine formed in dough through the action of yeast Sac-charomyces cerevisiae) is the main precursor of the typical aroma of bread crust, for which 2-acetyl-l-pyrroline together with 6-acetyl-l,2,3,4-tetrahydropyridine and its isomer 6-acetyl-2,3,4,5-tetrahydropyridine are responsible (see Section 8.2.12.4.1). 

Ornithine transcarbamylase has been found to occur in microorganisms S90, S96-401, 418), plants 419-421), yeast 422), and liver 404, 417, 423-429) and intestine 4II) of ureotelic animals. The enzyme has been partially purified from beef liver 417, 423), frog liver 406), E. coli 431), and Streptococcus lactis 4I8). Ornithine transcarbamylase shows a high substrate specificity 417, 423). The synthesis of the enz3nne is suppressed by arginine in E. coli 430, 431). 

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