Metabolism and Glycogen Regulation

This set of flashcards covers ATP synthesis mechanisms, glucose oxidation yields, and the detailed regulation of glycogen degradation through phosphorylase isozymes.

Glycerol phosphate shuttle

A mechanism used in muscles to shuttle electrons from cytoplasmic $NADH$ into the mitochondria.

ATP–ADP translocase

A transporter powered by the proton-motive force that enables the exchange of cytoplasmic $ADP$ for mitochondrial $ATP$.

ATP synthasome

A large complex formed by the association of the ATP–ADP translocase, the phosphate carrier, and the ATP synthase.

Complete oxidation of glucose (ATP yield)

The combustion of one molecule of glucose yields about $30$ molecules of $ATP$, where $26$ are formed in oxidative phosphorylation and $4$ are formed in glycolysis.

Acceptor control

Also known as respiratory control, this is the regulation of oxidative phosphorylation by the availability of $ADP$.

Glycogen

A highly branched homopolymer of glucose stored primarily in the liver and muscle tissues.

Glucose 6-phosphatase

An enzyme present in the liver, but absent in most other tissues, that generates free glucose from glucose 6-phosphate for release into the blood.

Phosphorylase a

The more active form of phosphorylase that is phosphorylated at serine residue $14$.

Phosphorylase b

The less active, non-phosphorylated form of phosphorylase.

Liver phosphorylase (Default state)

The default state is the $a$ form in the $R$ state, prepared to generate blood glucose unless signaled otherwise.

Muscle phosphorylase (Default state)

The default state is the $b$ form in the $T$ state, which is less active.

Allosteric regulation of muscle phosphorylase

The enzyme is shifted to the more active $R$ state by high $[AMP]$ and shifted to the less active $T$ state by high $[ATP]$ or $[glucose]$.

Allosteric regulation of liver phosphorylase

Glucose acts as a negative regulator, binding to the enzyme to stabilize the $T$ state and reduce activity.

Phosphodiesterase

An enzyme that converts $cAMP$ into $AMP$ to stop the stimulation of protein kinase A during the termination of glycogen degradation.

Protein phosphatase 1

An enzyme that inactivates glycogen degradation by removing phosphoryl groups from phosphorylase kinase and glycogen phosphorylase.