Scott R A, Beuman D E, Clark J H
J Dairy Sci. 1976 Jan;59(1):50-6. doi: 10.3168/jds.s0022-0302(76)84155-0.
The gluconeogenic capacity of mammary tissue of lactating cow was investigated by incubating mammary tissue slices with alanine, glutamate, lactate, pyruvate, or glycerol in conjunction with acetate and glucose (10mM or 1 mM). In no case was any substrate incorporated into glucose per se. In lactose synthesis, glucose was the major source of carbon although glycerol also was incorporated into lactose. Alanine, glutamate, lactate, or pyruvate were not incorporated into lactose at optimum (10 mM) or suboptimum (1 mM) concentrations of glucose. Activity of glucose-6-phosphatase was negligible in mammary tissue, less than 1% of the activity in liver or kidney tissue from the same cows. Pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose-1,6-diphosphatase were in cow mammary tissue, but the activities were lower than in liver. Gluconeogenic substrates were not converted to glucose regardless of whether the incubation contained an optimum (10 mM) or a suboptimum (1 mM) glucose concentration. Consistent with the inability of cow mammary tissue to convert gluconeogenic metabolites to glucose is the virtual absence of glucose-6-phosphatase and the lack of excess gluconeogenic substrates available to the intact mammary gland of lactating cow.
通过将泌乳奶牛的乳腺组织切片与丙氨酸、谷氨酸、乳酸、丙酮酸或甘油一起，结合乙酸盐和葡萄糖（10mM或1mM）进行孵育，研究了泌乳奶牛乳腺组织的糖异生能力。在任何情况下，都没有任何底物本身被掺入葡萄糖中。在乳糖合成中，葡萄糖是主要的碳源，尽管甘油也被掺入乳糖中。在葡萄糖的最佳（10mM）或次最佳（1mM）浓度下，丙氨酸、谷氨酸、乳酸或丙酮酸都没有被掺入乳糖中。葡萄糖-6-磷酸酶在乳腺组织中的活性可以忽略不计，不到同一头牛肝脏或肾脏组织中活性的1%。丙酮酸羧化酶、磷酸烯醇式丙酮酸羧激酶和果糖-1,6-二磷酸酶存在于奶牛乳腺组织中，但活性低于肝脏。无论孵育中葡萄糖浓度是最佳（10mM）还是次最佳（1mM），糖异生底物都不会转化为葡萄糖。与奶牛乳腺组织无法将糖异生代谢物转化为葡萄糖相一致的是，葡萄糖-6-磷酸酶几乎不存在，并且泌乳奶牛完整的乳腺缺乏过量的糖异生底物。
