Developmental changes in hepatic methionine adenosyltransferase, cystathionine β-synthase, cystathionase, and glycine N-methyltransferase were determined in broiler chick embryos and hatched chicks by using radiometric and spectrometric methods. Hepatic free methionine, S-adenosylmethionine, S-adenosylhomocysteine, homocysteine, cystathionine, and cysteine levels were also investigated. Results showed an increase in hepatic MAT activity from E10 to E21 during embryogenesis, suggesting greater transmethylation rates throughout the rapid embryonic growth and development period. A strong positive correlation between embryo BW and MAT activity also supports this idea. The MAT specific activity continued to increase after hatching, but there was a negative correlation between chick BW and MAT activities from D1 to D49. This may indicate different MAT isozymes exist for chick embryo hepatic tissue compared to hepatic tissue of hatched chick and growing broilers. The developmental pattern of MAT isozymes could be critical for methionine metabolism to cope with the demand imposed on the embryo, chicks, and growing broilers. Additionally, the specific activity of hepatic CBS in chick embryos was determined to be lower compared to that observed in older broilers (35 and 49 days). Since liver CBS specific activity is at the lowest point from D1-7 in young chicks, the ability to convert adequate homocysteine to cysteine through transsulphuration may be limiting for cysteine synthesis at this time. Steady-state hepatic homocysteine levels in chick embryos and chicks may be a function of the rates of homocysteine formation, remethylation, and catabolism via the transsulphuration pathway. The present study indicates young chicks from D1 to D7 may have a limited ability for adequate transsulphuration; therefore, dietary cystine may be needed for optimum performance.

中文翻译：

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E10-21 鸡胚和 D1-49 肉鸡肝蛋氨酸分解代谢酶活性（甲基化和转硫）和相关生理氨基酸的个体发育

使用辐射测定法和光谱测定法测定肉鸡胚胎和孵化的小鸡肝蛋氨酸腺苷转移酶、胱硫醚β-合酶、胱硫醚酶和甘氨酸N-甲基转移酶的发育变化。还研究了肝游离甲硫氨酸、S-腺苷甲硫氨酸、S-腺苷高半胱氨酸、高半胱氨酸、胱硫醚和半胱氨酸水平。结果显示，在胚胎发生过程中，肝脏 MAT 活性从 E10 增加到 E21，表明在整个快速胚胎生长和发育期间，转甲基化率更高。胚胎 BW 和 MAT 活性之间的强正相关也支持这个想法。孵化后MAT比活性继续增加，但从D1到D49雏鸡体重与MAT活性呈负相关。这可能表明与孵化鸡和生长肉鸡的肝组织相比，鸡胚肝组织存在不同的 MAT 同工酶。MAT 同工酶的发育模式对于蛋氨酸代谢以应对强加于胚胎、雏鸡和生长肉鸡的需求至关重要。此外，与在年龄较大的肉鸡（35 天和 49 天）中观察到的相比，鸡胚中肝脏 CBS 的比活性被确定为较低。由于肝脏 CBS 比活性在幼鸡中从 D1-7 开始处于最低点，因此此时通过转硫作用将足够的同型半胱氨酸转化为半胱氨酸的能力可能会限制半胱氨酸的合成。鸡胚和雏鸡中稳态肝同型半胱氨酸水平可能是同型半胱氨酸形成、再甲基化、和通过转硫途径分解代谢。本研究表明，从 D1 到 D7 的雏鸡进行充分转硫的能力可能有限；因此，可能需要膳食胱氨酸以获得最佳性能。