Tissues, especially skeletal muscle, contain this
-When ATP synthesis exceeds immediate needs

(high energy charge), creatine is converted to phosphocreatine.  When energy is needed (e.g., for a burst of activity), phosphocreatine is used to convert ADP to ATP. Phosphocreatine has a high energy

phosphate bond (~10.3 kcal/mol). 

One or two high-energy electrons

can be captured by FAD, forming FADH^• (a free

radical) or FADH₂. FADH₂ is oxidized by O₂ in

mitochondria to yield 1.5 ATP.

Two high energy electrons in the

form of hydride ion (H^- = H:) can be captured by

NAD⁺, forming NADH. Reoxidation of NADH by O₂

in mitochondria ultimately yields 2.5 ATP.

A central metabolic intermediate and a high

energy species that can transfer acetyl groups
(CH3-C(=O)^-) to other biological molecules or to

water. Other acyl groups can also be attached to CoASH to yield high energy thioesters

When enzymes for sequential steps are grouped so that the intermediates do not diffuse away.
-Such physically associated enzymes

are called a metabolon. 

Responsible for basal glucose uptake and are therefore found in nearly all mammalian tissues, particularly in neuronal cells and RBCs (GLUT1 only).  Their Km for 

glucose is 1 mM, so they are always saturated.

This catalyzes the phosphorolytic cleavage of the α(1-4) 

bonds of glycogen.
- The enzyme works only on non-reducing ends that are > 4 residues away from a branch point. 
- Glycogen phosphorylase contains an active site 

pyridoxal phosphate (PLP) residue that acts as a general acid-base catalyst (this is an atypical use of PLP).  

 Located on the luminal surface of the endoplasmic reticulum (ER), so G-6-P is transported out to it, and glucose is then transported back into the cytosol and 

then out into the plasma.
-this reaction occurs in liver, but not in skeletal muscle 

Catalyzes the committed and rate-determining

step of the pathway
 -catalyzes the conversion of fructose-6-phosphate to

fructose-1,6-bisphosphate (FBP)
-ATP acts as an inhibitor of the enzyme, its affect is to change the K_m of the enzyme for F6P, its substrate.
-Citrate, a central intermediate in the tricarboxylic acid (TCA) cycle, also serves as a feedback inhibitor in a manner similar to that of ATP
-AMP, ADP, and inorganic phosphate (P_i) act as allosteric activators (signaling a need for more ATP production) by competing with ATP for binding to the allosteric ATP site. 

Most important allosteric activator of PFK-1
-The concentration of fructose-2,6-bisphosphate is hormonally regulated by the balance between insulin and

glucagon (in the liver).
-The effect of fructose-2,6-bisphosphate is to modulate the Km of PFK-1 for its substrate fructose-6-phosphate and its inhibition by ATP. 

This enzyme forms fructose-2,6-bisphosphate from a small amount of fructose-6-phosphate
-shares a polypeptide chain with FBPase-2
-regulated allosterically by fructose-6-phosphate

and covalently by phosphorylation of a single serine residue within the regulatory domain by a protein kinase.  It is activated in its unphosphorylated form

F-2,6,-bP broken down to fructose-6-phosphate and P_i by the action of this enzyme, which is on the same polypeptide chain as PFK-2
-activities are reciprocally regulated allosterically by fructose-6-phosphate and covalently by phosphorylation of a single serine residue within the regulatory domain

by a protein kinase. 
-activated in its phosphorylated form 

Glucose is converted to a metabolically active form not recognized by GLUT transporters (G-6-P) in most cells by this kinase
-occurs in several tissue-specific isoforms but all are active toward a broad range of hexose sugars have a low Km for glucose (~0.1 mM), use Mg-ATP as the true nucleotide substrate, and are inhibited by

glucose-6-phosphate (an example of product inhibition). 

In the mitochondrion pyruvate is converted to oxaloacetate by this enzyme
-an ATP dependent enzyme
-used in gluconeogenesis to bypass the pyruvate kinase step of glycolysis, which is irreversible
-an allosterically regulated biotin-dependent enzyme
-Oxaloacetate cannot cross the mitochondrial membrane and must be reduced to malate by

mitochondrial malate dehydrogenase or converted to aspartate by aspartate aminotransferase (AAT). 

-during gluconeogenesis, this is synthesized by pyruvate carboxylase in the mitochondira to bypass the pyrukate kinase step of glycolysis
-cannot cross the mitochondrian membrane & must be reduced to malate by mitochondrial malate dehydrogenase or converted to aspartate by aspartate aminotransferase (AAT).
-Once in the cytosol, malate is reoxidized to

oxaloacetate by cytosolic malate dehydrogenase or Asp is reconverted to OAA by cytosolic AAT. 

Glucose is converted to G-6-P in liver and in pancreatic β-cells by this enzyme.  
-has a higher Vmax and also a higher Km for glucose than hexokinase (~10 mM).
-It is not inhibited by glucose-6-phosphate.

-Glucokinase expression is increased by insulin. 

Glycogen phosphorylase releases glucose-1-phosphate (G-1-P), but further metabolism requires glucose-6-phosphate (G-6-P). Phosphoglucomutase makes this

conversion.
-also used in the synthetic process, where it converts the opposite reaction of G-6-P to G-1-P