Connett R J
Am J Physiol. 1979 Nov;237(5):C231-6. doi: 10.1152/ajpcell.1979.237.5.C231.
The rates of 14carbon incorporation into CO2 and glycogen from [U-14C]-lactate and [1-14C]acetate in frog sartorius muscles were compared. The rates of incorporation into CO2 were similar, while the rate of incorporation of lactate into glycogen was more than 200-fold larger than that of acetate incorporation. It is concluded that the pathway of lactate incorporation into glycogen does not involve Krebs cycle intermediates and is extramitochondrial. To test the possibility that the pathway of lactate incorporation involves net reversal of a pyruvate kinase, the changes in phosphoenolpyruvate and pyruvate concentrations during stimulation of lactate incorporation into glycogen were measured. There wer none. The mass action ratio of pyruvate kinase was calculated. This value was two orders of magnitude from the equilibrium constant and it was concluded that reversal of pyruvate kinase was a very unlikely pathway. To test the possibility that a pathway involving the oxaloacetate-to-phosphoenolpyruvate step was involved the muscles were treated with 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase. The treatment resulted in decreased incorporation of lactate into glycogen.
比较了青蛙缝匠肌中[U-¹⁴C]-乳酸和[1-¹⁴C]乙酸盐的¹⁴C掺入二氧化碳和糖原的速率。掺入二氧化碳的速率相似，而乳酸掺入糖原的速率比乙酸盐掺入速率大200多倍。得出的结论是，乳酸掺入糖原的途径不涉及三羧酸循环中间产物，且是线粒体外的。为了测试乳酸掺入途径是否涉及丙酮酸激酶净逆转的可能性，测量了刺激乳酸掺入糖原过程中磷酸烯醇丙酮酸和丙酮酸浓度的变化。未发现变化。计算了丙酮酸激酶的质量作用比。该值与平衡常数相差两个数量级，得出结论，丙酮酸激酶逆转是极不可能的途径。为了测试涉及草酰乙酸到磷酸烯醇丙酮酸步骤的途径的可能性，用磷酸烯醇丙酮酸羧激酶抑制剂3-巯基吡啶甲酸盐处理肌肉。该处理导致乳酸掺入糖原减少。
