Vandercammen A, Van Schaftingen E
Laboratory of Physiological Chemistry, University of Louvain, Brussels, Belgium.
Biochem J. 1993 Sep 1;294 ( Pt 2)(Pt 2):551-6. doi: 10.1042/bj2940551.
Rat liver is known to contain a regulatory protein that inhibits glucokinase (hexokinase IV or D) competitively versus glucose. This inhibition is greatly reinforced by the presence of fructose 6-phosphate and antagonized by fructose 1-phosphate and by KCl. This protein was now measured in various rat tissues and in the livers of various species by the inhibition it exerts on rat liver glucokinase. Rat, mouse, rabbit, guinea-pig and pig liver, all of which contain glucokinase, also contained between 60 and 200 units/g of tissue of a regulatory protein displaying the properties mentioned above. By contrast, this protein could not be detected in cat, goat, chicken or trout liver, or in rat brain, heart, skeletal muscle, kidney and spleen, all tissues from which glucokinase is missing. Fructose 1-phosphate stimulated glucokinase in extracts of human liver, indicating the presence of regulatory protein. In addition, antibodies raised against rat regulatory protein allowed the detection of an approximately 60 kDa polypeptide in rat, guinea pig, rabbit and human liver. The livers of the toad Bufo marinus, of Xenopus laevis and of the turtle Pseudemys scripta elegans contained a regulatory protein similar to that of the rat, with, however, the major difference that it was not sensitive to fructose 6-phosphate or fructose 1-phosphate. In rat liver, the regulatory protein was detectable 4 days before birth. Its concentration increased afterwards to reach the adult level at day 30 of extrauterine life, whereas glucokinase only appeared after day 15. In the liver of the adult rat, starvation and streptozotocin-diabetes caused a 50-60% decrease in the concentration of regulatory protein after 7 days, whereas glucokinase activity fell to about 20% of its initial level. When 4-day-starved rats were refed, or when diabetic rats were treated with insulin, the concentration of regulatory protein slowly increased to reach about 85% of the control level after 3 days, whereas the glucokinase activity was normalized after the same delay. The fact that there appears to be no situation in which glucokinase is expressed without regulatory protein is in agreement with the notion that the regulatory protein forms a functional entity with this enzyme.
已知大鼠肝脏含有一种调节蛋白，该蛋白可与葡萄糖竞争性抑制葡萄糖激酶（己糖激酶IV或D）。6-磷酸果糖的存在会大大增强这种抑制作用，而1-磷酸果糖和氯化钾则可拮抗这种抑制作用。现在通过该蛋白对大鼠肝脏葡萄糖激酶的抑制作用来测定其在大鼠的各种组织以及不同物种肝脏中的含量。大鼠、小鼠、兔子、豚鼠和猪的肝脏都含有葡萄糖激酶，并且每克组织中还含有60至200个单位具有上述特性的调节蛋白。相比之下，在猫、山羊、鸡或鳟鱼的肝脏中，以及在大鼠的脑、心脏、骨骼肌、肾脏和脾脏（所有这些组织均缺乏葡萄糖激酶）中均未检测到这种蛋白。1-磷酸果糖可刺激人肝脏提取物中的葡萄糖激酶，这表明存在调节蛋白。此外，用针对大鼠调节蛋白产生的抗体可检测到大鼠、豚鼠、兔子和人肝脏中存在一种约60 kDa的多肽。海蟾蜍、非洲爪蟾和秀丽锦龟的肝脏含有一种与大鼠相似的调节蛋白，不过主要区别在于它对6-磷酸果糖或1-磷酸果糖不敏感。在大鼠肝脏中，出生前4天即可检测到调节蛋白。其浓度随后升高，在出生后第30天达到成年水平，而葡萄糖激酶仅在第15天后才出现。在成年大鼠肝脏中，饥饿和链脲佐菌素诱导的糖尿病会导致7天后调节蛋白浓度降低50 - 60%，而葡萄糖激酶活性降至初始水平的约20%。当饥饿4天的大鼠重新进食，或糖尿病大鼠用胰岛素治疗时，调节蛋白浓度在3天后缓慢升高，达到对照水平的约85%，而葡萄糖激酶活性在相同延迟后恢复正常。在没有调节蛋白的情况下似乎不存在葡萄糖激酶表达的情况，这一事实与调节蛋白与该酶形成功能实体的观点一致。
