presentasi_PIRUVAT_KINASE
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Transcript presentasi_PIRUVAT_KINASE
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].