桔獩椠?慣汬摥愠lim尠it branch “.
Debranching enzyme has 2 independent active sites, consisting of residues in different segments of a single polypeptide chain:
? Glucan transferase ? Alpha-1,6-glucosidase
Glycogen catabolism (breakdown):
Glycogen Phosphorylase catalyzes phosphorolytic cleavage of the ? (1?4) glycosidic linkages of glycogen, releasing glucose-1-phosphate as reaction product.
?
糖原是由多个葡萄糖组成的带分枝的大分子多糖，
分子量一般在106-107道尔顿，可高达108道尔顿，是体内
糖的贮存形式，糖原主要贮存在肌肉和肝脏中，肌肉中糖
原约占肌肉总重量的1-2%约为400克，肝脏中糖原占总量
6-8%约为100克。肌糖原分解为肌肉自身收缩供给能量，
肝糖原分解主要维持血糖浓度。
? Liver
glycogen (n residues) + Pi ? glycogen (n–1 residues) + glucose-1-phosphate
This phosphorolysis may be compared to hydrolysis:
Hydrolysis: R-O-R' + HOH ? R-OH + R'-OH
糖原的分解和生物合成
一、糖原的分解 二、糖原的生物合成 三、糖原代谢的调控
糖原( glycogen ) ，又称动物淀粉，支链，分子量 数百万以上。主要由葡萄糖以 α（1，4）糖苷键相 连（93%) ，以少量 α（1，6）糖苷键（ 7% ）形成分 支。有肝糖原和肌糖原。
Glycogen Functions
?The ? (1? 6) glucosidase moiety of the debranching enzyme then catalyzes hydrolysis of the ? (1?6) linkage, yielding free glucose. This is a minor fraction of glucose released from glycogen.
?The transferase of the debranching enzyme transfers 3 glucose residues from a 4-residue limit branch to the end of another branch, diminishing the limit branch to a single glucose residue.
– Buffer for regulating blood glucose levels
? Muscle
– Store of glucose as a fuel for exercise
? high intensity exercise dependent on anaerobic glycolysis
一、糖原的酶促磷酸解
? 糖原的结构及其连接方式
非还原性末端
? -1，6糖苷键
? -1，4-糖苷键
磷酸化酶a（催化1.4-糖苷键断裂） 三种酶协同作用： 转移酶（催化寡聚葡萄糖片段转移）
脱枝酶（催化1.6-糖苷键水解断裂）
CH2OH
H H OH
OH
O HH H
O
H
OH
CH2OH
OH
H
OH
H
1
O
H
OH
Glycogen Degradation
? Glycogen Phosphorylase
– Hydrolyzes glucose units from glycogen – Produces glucose-1-P
? Removal of branch points
– Debranching enzyme complex
Chapter13 Additional Pathways in Carbohydrate Metabolism
? Glycogen degradation and synthesis 糖原代谢与分解
? Gluconeogenesis 糖异生
? The pentose Phosphate pathway 磷酸戊糖途径
CH2OH
H
O
H
OH HOHFra bibliotekHH O
H
OH
CH2OH
O H OH H
H
OH
HH O4
6CH2 5 H OH
3 H
glycogen
O HH
H1
4
O
2
OH
CH2OH
O H OH H
H
OH
HH O
CH2OH
OH H OH H
OH
H
OH
Glycogen is a polymer of glucose residues linked by ? ? (1?4) glycosidic bonds, mainly ? ? (1?6) glycosidic bonds, at branch points. Glycogen chains & branches are longer than shown. Glucose is stored as glycogen predominantly in liver and muscle cells.
Phosphorolysis:
R-O-R'
+
HO-PO
23
?
R-OH
+
R'-O-PO
23
A glycogen storage site on the surface of the Phosphorylase enzyme binds the glycogen particle.
Given the distance between storage & active sites, Phosphorylase can cleave ? (1?4) linkages only to within 4 residues of an ? (1?6) branch point.