Eka Susilawati
Sukmawati Ayu
Martalia Wahyu
Hasan Ramdan
Tiara Pelangi A
Sri Aryani
(10506106)
(10507032)
(10507034)
(10507056)
(10507066)
(10507076)
Three Glycolysis reactions have such a large
negative DG that they are essentially irreversible.
 Hexokinase (or Glucokinase)
 Phosphofructokinase
 Pyruvate Kinase.
Pyruvate Kinase (last step of Glycolysis) catalyzes:
phosphoenolpyruvate + ADP  pyruvate + ATP

Piruvat Kinase adalah enzim yang
mengkatalisis langkah irreversibel ketiga
pada glikolisis

Piruvat Kinase menghasilkan ATP dan
Piruvat

Bila muatan energi tinggi , ATP secara
allosterik menginhibisi Piruvat Kinase untuk
memperlambat glikolisis
Piruvat Kinase
terfosforilasi
(kurang aktif)
H2O
Kadar
glukosa
darah merah
-
PI
+
ADP
ATP
Piruvat Kinase
terdesfosforilasi
(lebih aktif)
Fosfoenolpiruvat + ADP
+H+
+
Fruktosa 1,6bisfosfat
ATP
Alanin
Piruvat + ATP

Alanin secara allosterik menghambat piruvat
kinase

Bila kadar glukosa darah menurun, glukagon
memicu kaskade AMP siklik yang
menyebabkan fosforilasi Piruvat Kinase, yang
mengurangi aktivitasnya

Fosforilasi ini seperti enzim bifungsi yang
mengontrol kadar fruktosa 2,6-bisfosfat

Fruktosa 2,6-bisfosfat dibentuk melalui fosforilasi senyawa
fruktosa 6-fosfat oleh enzim fosfofruktokinase-2

dalam keadaan glukosa yang berlimpah, konsentrasi
senyawa fruktosa 2,6-bisfosfat akan meningkat sehingga
merangsang glikolisis dengan mengaktifkan
fosfofruktokinase-1 dan menghambat fruktosa-1,6bisfosfatase.

Dalam keadaan kekurangan glukosa, glukoneogenesis
dirangsang oleh penurunan konsentrasi fruktosa 2,6-bisfosfat
yang kemudian menghilangkan aktivitas fosfofruktokinase-1
dan meniadakan penghambatan kerja fruktosa-1, 6bisfosfatase.

Pyruvate Carboxylase
(pyruvate oxaloactate)
is allosterically activated by acetyl CoA.

[Oxaloacetate] tends to be limiting for
Krebs cycle.
G lucose-6-phosphatase
glucose-6-P
glucose
G luconeogenesis
G lycolysis
pyruvate
fatty acids
acetyl C oA
oxaloacetate
ketone bodies
citrate
K rebs C ycle
Enzymes relevant to these pathways that are
phosphorylated by Protein Kinase A include:
 Pyruvate Kinase, a glycolysis enzyme that is inhibited
when phosphorylated.
 CREB (cAMP response element binding protein) which
activates, through other factors, transcription of the
gene for PEP Carboxykinase, leading to increased
gluconeogenesis.
 A bi-functional enzyme that makes and degrades an
allosteric regulator, fructose-2,6-bisphosphate.

PFK activity in the presence of the globally controlled
allosteric regulator fructose-2,6-bisphosphate is similar to that
at low ATP.

Fructose-2,6-bisphosphate promotes the relaxed state,
activating Phosphofructokinase even at high [ATP].

Thus activation by fructose-2,6-bisphosphate, whose
concentration fluctuates in response to external hormonal
signals, supersedes local control by [ATP].