Methionine acid—base balance

Hydantoinase-Carbamoylase System for t-Amino Acid Synthesis Despite a number of reports of strains with L-selechve hydantoin-hydrolyzing enzymes [38] the commercial application of the hydantoinase process is stiU restricted to the production of D-amino acids. Processes for the production of L-amino acids are Umited by low space-time yields and high biocatalyst costs. Recently, a new generation of an L-hydantoinase process was developed based on a tailor-made recombinant whole cell biocatalyst. Further reduction of biocatalyst cost by use of recombinant Escherichia coli cells overexpressing hydantoinase, carbamoylase, and hydantoin racemase from Arthrohacter sp. DSM 9771 were achieved. To improve the hydan-toin-converting pathway, the level of expression of the different genes was balanced on the basis of their specific activities. The system has been appUed to the preparation of L-methionine the space-time yield is however still Umited [39]. Improvements in the deracemization process from rac-5-substituted hydantoins to L-amino acids still requires a more selective L-hydantoinase. 

The Sulfur Balance for Wool. Simmonds (1956) obtained a satisfactory sulfur balance for wool when cystine was determined as cysteic acid by the method of Schram et al. (1954) and both hydriodic acid-reducible sulfur and methionine were included in the sulfur balance. A micromethod for cystine determination based on the Shinohara (1935, 1936) method, however, gave values for total sulfur in amino acids 17 % higher than the results of sulfur analysis on wool. 

Nakagawa, I., Takahashi, T., and Suzuki, T. (1961). Amino acid requirements of children Minimal needs of lysine and methionine based on the nitrogen balance method. J. Nutr. 74, 401-407. 

Pig and poultry diets based on cereals and vegetable protein sources are now routinely supplemented with L-lysine hydrochloride (supplying 780 g lysine/kg), dl-methionine and L-threonine. A diet for a finishing pig, which has to contain 10 g lysine/kg, required a combination of 750 g barley and 250 g soya bean meal/kg, and this mix has a crude protein content of 185 g/kg (see Appendix 2, Table A.2.2.2). With the inclusion of 2 g of lysine hydrochloride, the same lysine content can be achieved with a mix of 808 g barley and 190 g soya bean meal, and the protein content is reduced to 165 g/kg. Such reductions in crude protein content have maintained a balanced supply of amino acids and resulted in improved rates of liveweight gain and food conversion efficiency. It is important that the supplementary acids are not used excessively to satisfy the animal s requirements, since this may bring about an undersupply of other essential amino acids. 

It is well known that methionine (Met) and lysine (Lys) are two of the most limiting amino acids (AA) for milk and protein production in lactating dairy cows fed corn-based diets (Schwab et al., 2003 Rulquin, 2004). The NRC (2001) suggested concentrations of Met and Lys of 2.4% and 7.2% on a metabolizable protein (MP) basis, respectively, in order to maximize the use of MP for milk and milk protein yield by lactating dairy cows. However, it should be taken in consideration that these concentrations are hardly achieved. Nutritionists have two methods to fed lactating dairy cows with AA balanced diets one is to incorporate feeds with a high level of rumen undegradable protein, and the other is to supplement the diet with ruminally protected (RP) synthetic AA (Schwab et al., 2003). The aim of this work was to assess the bioavadabUity of a RP D,L-Met and a RP L-Lys HCl products by a standardized blood test (Sudekum et al., 2004). 

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