Heinrich P C, Morris H P, Weber G
Cancer Res. 1976 Sep;36(9 pt.1):3189-97.
The objective of this investigation was to throw light on the biological behavior and metabolic regulation of hepatic enzymes of the nonoxidative branch of the pentose phosphate pathway. The activities of transaldolase (EC 2.2.1.2) and trasketolase (EC 2.2.1.1) Were compared in biological conditions that involve modulation of gene expression such as in starvation, in differentiation, after partial hepatectomy, and in a spectrum of hepatomas of different growth rates. The enzyme activities were determined under optimal kinetic conditions by spectrophotometric methods in the 100,000 X g supernatant fluids prepared from tissue homogenates. The kinetic properties of transaldolase and transketolase were similar in normal liver and in rapidly growing hepatoma 3924A. For transaldolase, apparent Km values of 0.13 mM (normal liver) and 0.17 mM (hepatoma) were observed for erythrose 4-phosphate and of 0.30 to 0.35 mM for fructose 6-phosphate. The pH optima in liver and hepatoma were at approximately 6.9 to 7.2. For the transketolase substrates, ribose 5-phosphate and xylulose 5-phosphate, the apparent Km values were 0.3 and 0.5 mM, respectively, in both liver and hepatoma. A broad pH optimum around 7.6 was observed in both tissues. In organ distribution studies, enzyme activities were measured in liver, intestinal mucosa, thymus, kidney, spleen, brain, adipose tissue, lung, heart, and skeletal muscle. Taking the specific activity of liver as 100%, transaldolase activity was the highest in intestinal mucosa (316%) and in thymus (219%); it was the lowest in heart (53%) and in skeletal muscle (21%). Transketolase activity was highest in kidney (155%) and lowest in heart (26%) and skeletal muscle (23%). Starvation decreased transaldolase and transketolase activities in 6 days to 69 and 74%, respectively, of those of the liver of the normal, fed rat. This was in the same range as the decrease in the protein concentration (66%y. In the liver tumors, transaldolase activity was increased 1.5- to 3.4-fold over the activities observed in normal control rat liver. Transketolase activity showed no relationship to tumor proliferation rate. In the regenerating liver at 24 hr after partial hepatectomy, the activity of both pentose phosphate pathway enzymes was in the same range as that of the sham-operated controls. In differentiation at the postnatal age of 5, 12, 23, and 32 days, hepatic transaldolase activities were 33, 44, 55, and 72%, respectively, of the activities observed in the 60-day-old, adult male rat. During the same period, transketolase activ-ties were 18, 21, 26, and 55% of the activities observed in liver of adult rat. The demonstration of increased transaldolase activity in hepatomas, irrespective of the degree of tumor malignancy, differentiation, or growth rate, suggests that the reprogramming of gene expression in malignant transformation is linked with an increase in the expression of this pentose phosphate pathway enzyme...
本研究的目的是阐明磷酸戊糖途径非氧化分支中肝酶的生物学行为和代谢调节。在涉及基因表达调节的生物学条件下，如饥饿、分化、部分肝切除术后以及不同生长速率的一系列肝癌中，比较了转醛醇酶（EC 2.2.1.2）和转酮醇酶（EC 2.2.1.1）的活性。通过分光光度法在由组织匀浆制备的100,000×g上清液中，在最佳动力学条件下测定酶活性。转醛醇酶和转酮醇酶在正常肝脏和快速生长的肝癌3924A中的动力学性质相似。对于转醛醇酶，观察到对磷酸赤藓糖的表观Km值在正常肝脏中为0.13 mM，在肝癌中为0.17 mM，对磷酸果糖的表观Km值为0.30至0.35 mM。肝脏和肝癌中的pH最适值约为6.9至7.2。对于转酮醇酶的底物磷酸核糖和磷酸木酮糖，在肝脏和肝癌中的表观Km值分别为0.3和0.5 mM。在两种组织中均观察到约7.6的宽pH最适值。在器官分布研究中，在肝脏、肠黏膜、胸腺、肾脏、脾脏、大脑、脂肪组织、肺、心脏和骨骼肌中测量酶活性。以肝脏的比活性为100%，转醛醇酶活性在肠黏膜中最高（316%），在胸腺中（219%）；在心脏中最低（53%），在骨骼肌中（21%）。转酮醇酶活性在肾脏中最高（155%），在心脏中最低（26%），在骨骼肌中（23%）。饥饿6天后，转醛醇酶和转酮醇酶活性分别降至正常喂食大鼠肝脏的69%和74%。这与蛋白质浓度的下降（66%）处于同一范围。在肝癌中，转醛醇酶活性比正常对照大鼠肝脏中观察到的活性增加了1.5至3.4倍。转酮醇酶活性与肿瘤增殖速率无关。在部分肝切除术后24小时的再生肝脏中，磷酸戊糖途径两种酶的活性与假手术对照组处于同一范围。在出生后5、12、23和32天的分化过程中，肝脏转醛醇酶活性分别为60日龄成年雄性大鼠肝脏中观察到活性的33%、44%、55%和72%。在同一时期，转酮醇酶活性分别为成年大鼠肝脏中观察到活性的18%、21%、26%和55%。肝癌中转醛醇酶活性增加的证明，无论肿瘤的恶性程度、分化程度或生长速率如何，表明恶性转化中基因表达的重编程与该磷酸戊糖途径酶表达的增加有关……
