Influence of Level and Source of Nitrogen Intake on Liver Glutamine Synthetase Activity in the Chick

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Abstract
Studies were conducted with chicks on the influence of level and source of dietary nitrogen on hepatic glutamine synthetase activity. Chicks fed a 75% isolated soybean protein (ISP) diet for 10 days exhibited a fourfold increase in enzyme activity as compared with chicks fed a 25% ISP diet. Glutamine synthetase activity increased threefold during the first 24 hours chicks were fed the 75% ISP diet, remained at about this level for days 2 and 3 and increased slightly at day 4. The addition of 25% ISP or its nitrogen equivalent as diammonium citrate, glutamic acid or diammonium citrate + glutamic acid resulted in a significant increase (P < 0.05) in enzyme activity over that of chicks fed the 25% ISP diet. Feeding the diet containing both diammonium citrate and glutamic acid resulted in a moderate increase in enzyme activity over that observed when an isonitrogenous amount of diammonium citrate was fed singly. It is suggested that both substrates, ammonia and L-glutamate, act synergistically in the regulation of glutamine synthetase; a possible role of transdeamination as a mechanism involved in the regulation of glutamine synthetase in the chick is discussed.