Departamento de Biología Aplicada, Escuela Politécnica Superior, Universidad de Almería, Almería, Spain.
Fish Physiol Biochem. 2012 Jun;38(3):859-69. doi: 10.1007/s10695-011-9573-1. Epub 2011 Nov 16.
After the development of the gastric function in juvenile fish, dietary proteins enter a two-phase digestive process comprising an acidic gastric phase followed by an alkaline intestinal phase. However, the main gastric protease, pepsin, is strictly dependent on the existence of a low-enough environmental pH. In 20-g gilthead sea bream, Sparus aurata, the mean minimal gastric pH is close to 4.5, while the mean pH in the duodenal portion of the intestine was nearly fixed at 6.5. The mean maximal gastric content of HCl was approximately 20 microEq for a low-buffering diet. Gastric proteases were more severely affected than intestinal proteases when assayed at actual sub-optimal pH values, 4.5 and 6.5, respectively. When the gastric proteases of juvenile fish were pre-incubated with a citric acid buffer at pH 6.0, the activity at pH 4.5 was very low, whereas when they were pre-incubated with the same buffer at pH 3.0, the activity at pH 4.5 was significantly increased; this fact suggests a deficient activation of zymogens during the gastric digestion and points to a potential approach to improve protein digestion in juvenile gilthead sea bream.
在幼鱼的胃功能发育后，膳食蛋白质进入一个两相消化过程，包括酸性胃相和碱性肠相。然而，主要的胃蛋白酶，胃蛋白酶，严格依赖于足够低的环境 pH 值的存在。在 20 克重的金头鲷，Sparus aurata 中，平均最小胃 pH 值接近 4.5，而肠的十二指肠部分的平均 pH 值几乎固定在 6.5。对于低缓冲饮食，盐酸的平均最大胃含量约为 20 微当量。当在实际亚最佳 pH 值 4.5 和 6.5 下测定时，胃蛋白酶比肠蛋白酶受到更严重的影响。当幼鱼的胃蛋白酶在 pH 6.0 的柠檬酸缓冲液中预孵育时，在 pH 4.5 时的活性非常低，而当它们在 pH 3.0 的相同缓冲液中预孵育时，在 pH 4.5 时的活性显著增加；这一事实表明在胃消化过程中酶原的激活不足，并指出了一种提高幼年金头鲷蛋白质消化的潜在方法。
