第26章 糖原的分解与合成 Degradat ion and Synthesis of Glycogen
第 26 章 糖原的分解与合成 Degradation and Synthesis of Glycogen
糖原的分解代谢 1. Glycogen in cells is first converted to Glc-6-P for oxidative degradation ★糖原磷酸化酶作用于糖原的非还原性末端, 经磷酸解作用,产生Gc-1-P。 ★糖原磷酸化酶的辅基磷酸吡哆醛直接作用 于(α-1,4)糖苷键 ★在距分支点四个糖单位处,糖原磷酸化酶 停止磷酸解作用
一、糖原的分解代谢 1. Glycogen in cells is first converted to Glc-6-P for oxidative degradation: ★ 糖原磷酸化酶作用于糖原的非还原性末端， 经磷酸解作用，产生 Glc-1-P 。 ★ 糖原磷酸化酶的辅基磷酸吡哆醛直接作用 于(a-1,4) 糖苷键。 ★ 在距分支点四个糖单位处，糖原磷酸化酶 停止磷酸解作用
★转移酶( a bifunctional debranching enzyme)(160kD)转移一个分支点的三个 糖单位到另一个非还原末端,脱枝酶(α 1,6- glucosidase)脱去分支点的葡萄糖。 x Glc-1-P is then converted to Glc-6-p by the catalysis of phosphoglucomutase, which uses glucose 1, 6-bisphosphate as both a cofactor and an intermediate an ser residue on the enzyme facilitates the phosphorylation cycle Glc-6-P is further degraded via the glycolysis pathway(or converted to glucose in liver)
★ 转移酶（ A bifunctional debranching enzyme ） (160 kD)转移一个分支点的三个 糖单位到另一个非还原末端， 脱枝酶（ a- 1,6- glucosidase ）脱去分支点的葡萄糖。 ★ Glc-1-P is then converted to Glc-6-P by the catalysis of phosphoglucomutase, which uses glucose 1,6-bisphosphate as both a cofactor and an intermediate. An Ser residue on the enzyme facilitates the phosphorylation cycle. ★ Glc-6-P is further degraded via the glycolysis pathway (or converted to glucose in liver)
2. The glycogen phosphorylase isozymes in muscle and liver are regulated and differently ◆肌糖原和肝糖原的生理功能不同:前者主要是 氧化供能( oxidative degradation to generate ATP for muscle),而肝糖原主要用于维持血 糖浓度( producing and exporting glucose when in demand and importing and storing When in excess ◆肌糖原磷酸化酶和肝糖原磷酸化酶为同工酶 者的活性均受磷酸化(cata! yzed by specific phosphorylase b kinase)和脱磷酸 catalyzed by specific phosphorylase a phosphatase)共价可逆调控
2. The glycogen phosphorylase isozymes in muscle and liver are regulated and differently ◆肌糖原和肝糖原的生理功能不同：前者主要是 氧化供能（ oxidative degradation to generate ATP for muscle ），而肝糖原主要用于维持血 糖浓度（producing and exporting glucose when in demand and importing and storing when in excess）. ◆ 肌糖原磷酸化酶和肝糖原磷酸化酶为同工酶， 二者的活性均受磷酸化（ catalyzed by specific phosphorylase b kinase ）和脱磷酸 （ catalyzed by specific phosphorylase a phosphatase ）共价可逆调控
The phosphorylase b kinases in muscle and liver are controlled by two different hormones, epinephrine(肾上腺素)and g! ucagon(胰增血糖素) respectively.D High level of amp binds to and activates the b form of the muscle isozyme which is blocked by a high level of aTp High level of glucose binds to the a form of the liver isozyme exposing the phosphorylated ser residues to the action of phosphorylase a phosphatase and converting it to the less active b form
◆ The phosphorylase b kinases in muscle and liver are controlled by two different hormones, epinephrine (肾上腺素) and glucagon(胰增血糖素) respectively. • ◆ High level of AMP binds to and activates the b form of the muscle isozyme, which is blocked by a high level of ATP. • ◆ High level of glucose binds to the a form of the liver isozyme, exposing the phosphorylated Ser residues to the action of phosphorylase a phosphatase and converting it to the less active b form