Farrow S M, Jones C T
Biochem J. 1986 Apr 1;235(1):103-10. doi: 10.1042/bj2350103.
During analysis of pyruvate kinase distribution in developing guinea-pig liver it was observed that a substantial proportion of the activity remained associated with the microsomal membrane fraction ('microsomes'). Although some of this could be removed by washing with sucrose, the majority required detergent treatment for liberation, and even then at least one-half remained attached to the microsomes. Estimates of the contribution of this fraction to total cell pyruvate kinase activity indicated that it was more than 50% of the total, and this is likely to be an underestimate because of the continued latency of the enzyme even in the presence of detergent. The susceptibility of the microsomal enzyme, whether released by detergent or sucrose washing, to inactivation by Triton X-100 suggested it to be different from the cytosolic enzyme, which was stable under such conditions. (The microsomal enzyme required the presence of additional protein, such as bovine serum albumin, to maintain stability.) This view was confirmed by DEAE-cellulose chromatography and particularly isoelectric focusing, where the microsomal enzyme was shown to consist of at least four forms, which were distinctly different from those in the cytosol. Those data and the kinetic properties of the four forms in the membrane fraction indicate that the microsomal pyruvate kinase could consist of four counterparts to the cytosolic isoenzyme forms. These results are discussed in relation to the two possible explanations for the phenomenon (not mutually exclusive): that the more hydrophobic membrane forms are precursors of the cytosolic enzyme and that they may be part of functional glycolytic pathway in the microsomes of developing liver.
在分析豚鼠发育肝脏中丙酮酸激酶的分布时，观察到相当一部分活性仍与微粒体膜部分（“微粒体”）相关。尽管其中一些可以通过用蔗糖洗涤去除，但大多数需要用去污剂处理才能释放出来，即便如此，至少仍有一半附着在微粒体上。对该部分对细胞总丙酮酸激酶活性贡献的估计表明，它占总量的50%以上，而且由于即使在有去污剂存在的情况下该酶仍持续存在潜伏性，这可能是一个低估。微粒体酶（无论是通过去污剂释放还是蔗糖洗涤释放）对Triton X - 100失活的敏感性表明它与胞质酶不同，胞质酶在这种条件下是稳定的。（微粒体酶需要有额外的蛋白质，如牛血清白蛋白，来维持稳定性。）通过DEAE - 纤维素色谱法，特别是等电聚焦法证实了这一观点，在等电聚焦中显示微粒体酶至少由四种形式组成，这些形式与胞质中的明显不同。这些数据以及膜部分中四种形式的动力学特性表明，微粒体丙酮酸激酶可能由胞质同工酶形式的四种对应物组成。针对该现象的两种可能解释（并非相互排斥）对这些结果进行了讨论：疏水性更强的膜形式是胞质酶的前体，以及它们可能是发育中肝脏微粒体中功能性糖酵解途径的一部分。
