Download Control of intra-cellular (enzyme regulator)

CONTROL OF
CARBOHYDRATE METABOLISM
Control of metabolism can be simplified into:
a) Control of intra-cellular (enzymes regulator)
b) Systemic control (blood glucose)
Control by enzymes activity
An idealized cell in steady state. Note that
metabolite flow is unidirectional.
Despite the existence of short-term oscillations in
metabolite concentrations and enzyme levels,
living cells exist in a dynamic steady state in
which the mean concentrations of metabolic
intermediates remain relatively constant over time
COMPARTMENTATION ENSURES
METABOLIC EFFICIENCY &
SIMPLIFIES REGULATION
In eukaryotes, anabolic and
catabolic pathways that
interconvert common products
may take place in
specific sub cellular
compartments.
Enzymes that degrade proteins and
polysaccharides reside inside
organelles called lysosomes.
Fatty acid biosynthesis occurs in the
cytosol, whereas fatty acid oxidation
takes place within mitochondria
Segregation of certain metabolic
pathways within specialized cell
types can provide further physical
compartmentation.
Controlling an Enzyme That Catalyzes a
Rate-Limiting Reaction
Regulates an Entire Metabolic Pathway
While the flux of metabolites through
metabolic pathways involves catalysis by
numerous enzymes, active control of
homeostasis is achieved by regulation of only
a select subset of these enzymes.
The ideal enzyme for regulatory
intervention is one whose quantity or
catalytic efficiency dictates that the
reaction it catalyzes is slow relative to all
others in the pathway
Quantity:
synthesis
degradation
Synthesis in response to:
metabolite
hormone
Degradation:
damage to a prosthetic group
covalent modifications
allosteric effectors
2 ADP  ATP + AMP
Adenylyl kinase
Utilization of ATP will increase amount of AMP
Pyruvate Carboxylase :
↑ synthesis During fasting
activated by FFA and Acetyl-CoA
During fasting or starvation (DM):
↓activity of glycolysis, glycogenesis,
HMP Shunt uronic acid path way
↑act. Glycogenolysis gluconeogenesis
Carbohydrate metabolism
Glucose turnover (basal state)
55% Oxidation
45% Brain
10% Muscle
75%
Glycogenolysis
Glucose
25%
Gluconeogenesis
60% from lactate
20% Glycolysis
(muscle)
25% Re-uptake
(liver, gut)
Blood glucose :
↑ gluconeogenesis, glycogenolysis, diet
↓ glycolysis, glycogenesis, HMP Shunt,
uronic path way