bioenergetics

Pyruvate formed during metabolism of glucose can have ___fates

2

If pyruvate remains in cytosol, it is reduced to lactate by ____ _____

lactic dehydrogenase (LDH)

If pyruvate enters mitochondria, it can be oxidized to the two carbon compounded acetyl-CoA by the action of the _____ _____

pyruvate dehydrogenase complex (PDH)

pyruvate dehydrogenase complex (PDH)

The oxidative decarboxylation of pyruvate to acetyl CoA is catalyzed by the ___ ___ ___ an organized assembly consisting of three different enzymes. (in mitochondria). it is oxidative carboxylation.

overall reaction catalyzed by the pyruvate dehydrogenase complex is:

pyruvate + HS-CoA + NAD+ -> acetyl-CoA + CO2 + NADH

The reaction mechanism of pyruvate dehydrogenase entails ____ and ____

catalytic cofactors and stoichiometric cofactors

catalytic cofactors

thiamine pyrophosphate (TPP; vitamin B1), lipoamide, and FAD. they are regenerated during the enzyme cycle.

stoichiometric cofactors

Hs-CoA and NAD and they show in the overall equation

three enzymes

Pyruvate dehydrogenase is a multienzyme complex containing ___ ____ that catalyzes four steps leading to the final formation of acetyl-CoA

First Step: (E1)

Pyruvate dehydrogenase (E1) TPP

Second Step: (E2)

Dihydrolipoyl transacetylase (E2) Lipoamide

Third Step: (E3)

Dihydrolipoyl dehydrogenase (E3) FAD

pyruvate +HS-CoA+NAD+ -->(PDH)---> acetyol-CoA + CO2+ NADH

Acetyl-CoA and NADH inhibit PDH

the energy status of the cell controls

PDH activity

When cell is rich in available energy (lots of ATP or GTP inc.), the activity of the PDH complex is

reduced

When the cell's energy stores are low ( inc. AMP), PDH is

activated

we dont need more energy

GTP inhibits PDH

AMP is high; the complex

AMP stimulates PDH

The enzyme complex is ___ in the non-phosphorylated form

active

The enzyme complex is _____ when phosphorylated on the E1 subunit

inactive

Pyruvate dehydrogenase kinase (PDK)

catalyzes the conversion of the active (non-phosphorylated) to the inactive (phosphorylated) forms of PDH

Pyruvate dehydrogenase kinase activity

is stimulated by high ratios of ATP/ADP, acetyl CoA/CoA, and NADH/Nad+ and inhibited by pyruvate

protein phosphatase 1 (PPase)

The enzyme complex becomes active again when the phosphoryl group is removed by, which is stimulated by high levels of Ca2+ and insulin

liver

insulin activates the phosphatase in adipose tissue but not in ____

Protein Phosphatase 1

is involved in the regulation of glycogenolysis and glycogenesis. insulin stimulates protein phosphatase 1, thereby inhibiting the degradation of glycogen and activating the synthesis of glycogen

insulin will always act on

protein phosphatase 1

pyruvate dehydrogenase generates acetyl-CoA from pyruvate

originating from glycolysis

other sources of acetyl-CoA

fatty acid oxidation and certain amino acids.

fates of acetyl-CoA generated in the mitochondrial matrix include

a) complete oxidation of the acetyl group in the tricarboxylic acid cycle

b) conversion of excess acetyl CoA into ketone bodies (in the liver)

c) transfer of acetyl units to the cytosol for the synthesis of sterols and long-chain fatty acids

stage iii

acetyl-CoA is condensed with a component in the TCA

ATP is being formed

The primary metabolic fate of acetyl-CoA produced is its complete oxidation in the

tricarboxylic acid (or citric acid cycle or Krebs cycle) to CO2

Primary function of the tricarboxylic acid cycle (TCA) is to generate reducing equivalents

NADH and FADH2 that are utilized in the mitochondria electron-transport chain to generate ATP through oxidative phosphorylation

the control points of the TCA

Citrate synthase, isocitrate DH, α-ketoglutarate DH complex

the first control point

determined by the synthesis of citrate from oxaloacetate and acetyl CoA.

in the first control point,

ATP inhibits citrate synthase

second control point is

isocitrate synthase, stimulated by ADP

in the second control point,

it is inhibited by NADH and ATP

third control point

a-ketoglutarate dehydrogenase

in the third control point

a-ketoglutartarate dehydrogenase, is inhibited by the products of the reaction succinyl CoA and NADH

succinate (immediate) in is

mitochondria

SUCNR1 (in plasma membrane)

it elicits pro inflammatory reactions an example being diabetes, ischemia/reperfusion, oxidative stress

d

succinate-SUCRN1 signaling serves as a link between ___ _____ and ____

metabolic stress and inflammmation

during this pro-inflammatory response

COX2 increases and H1F1a triggers an increase of IL1B

elicits an anti-inflammatory reaction

itaconate

with the anti-inflammatory, itaconate

the anti-inflammatory cytokines increase, and the oxidative stress decreases

oxaloacetate

immediate for glucose formation

oxaloacetate is converted to

P-enol pyruvate; then converted to glucose

pyruvate to acetyl-CoA is called

pyruvate oxidation

when acetyl-CoA leaves the mitochondria it becomes

citrate

citrate acts as an intermediate for the synthesis of

fatty acids are sterols

pyruvate dehydrogenase deficiency

Must prevent the conversion of pyruvate to lactic acid since can't go to acetyl CoA (causes lactic acidosis otherwise).

pyruvate dehydrogenase deficiency symptoms

in children exhibit elevated plasma levels of lactate, pyruvate, and alanine, which produce chronic lactic acidosis and serious neurological defects that can result in death

diagnosis of PDH deficiency

assessing PDH activity in cultured skin fibroblasts from the patient

Treatment of PDH deficiency

ketogenic diet (ketones are an alternative source of energy)

improvement with dichloroacetate, an inhibitor of pyruvate dehydrogenase kinase, thus preventing inactivation of the enzyme complex

there are currently 2 NIH clinical trials on PDH deficiency: one advocates _____ treatment and another ___

phenylbutyrate, dicholoroacetate

ketogenic diet

produces ketone bodies which can make acetyl-CoA

Beri-Beri

is due to a deficiency of thiamine (vitamin B1) in the diet.

Beri-Beri deficiency can cause

neurologic and cardiovascular symptoms, including edema and heart enlargement

Beri-Beri is still a health problem in some parts of ___ with malnourished populations in the Western world (especially with alcoholics)

Asia

Vitamin B1 is a TPP (thiamine pyrophosphate),

a prostetic group of pyruvate dehydrogenase, a-ketoglutarate dehydrogenase (TCA cycle), and transketolase (pentose phosphate pathway)

In beri-beri the serum levels of pyruvate and a-ketoglutarate are

high

Beri-beri condition is diagnosed by the low activity of transketolase (which requires TPP) in

erythrocytes

the components of the mitochondrial respiratory chain are

complexes (I to V) and two mobile carriers: coenzyme Q and cytochromes

These components of the mitochondrial respiratory chain are

embedded in the inner membrane

Four large complexes linked by two mobiles carriers arranged in a sequential pattern in the IMM according to their

reduction potentials

NADH electrons enter at

complex I

Complex II (succinate dehydrogenase)

contains a flavoprotein: FP2

Complex III

cytochrome b-c1

complex IV

cytochrome oxidase contains cytochromes a and a3

Complex II

reaction of TCA; not embedded in the membrane

coenzyme q

fph (flavoproteins) donates electrons

reducing equivalents enter at the level of either complex I (electrons in the form of ____) or coenzyme Q (electrons from ____)

NADH, FPH2

coenzyme Q donates the electrons to ____ and this to the mobile carrier ____ ___

complex III, cytochrome c

electrons from cytochrome c are channeled to

complex IV, where they are used to reduce 02 to h20

rotenone (a fish poison) and amytal (a barbiturate) inhibit at the level of

Complex I

Antimycin A inhibits electron transfer at the ____ ___ site

Complex III

Complex IV or cytochrome oxidase is inhibited by

cyanide, azide, and carbon monoxide

Cyanide (CN-) (as hydrogen cyanide gas or KCN

is one of the most potent acting poisons known; it causes rapid inhibition of the mitochondrial electron transport

Cyanide

binds to the Fe3+ in the heme of the cytochrome aa3 of complex IV, thus preventing 02 from acting with aa3: mitochondrial respiration and energy production case and cell death occurs rapidly.

Death to CN- poisoning occurs from tissue asphyxia-

most notably of the central nervous system

CN has an affinity for

Complex IV; no O2 here

In complex IV the 02 binding site is reduced to

water

If cyanide poisoning is diagnosed rapidly, the patient can be given various

nitrites (NO2-) that convert oxyhemoglobin to methemoglobin (thus faciliating the conversion of the Fe2+ in hemoglobin to Fe3+ in methemoglobin)

Methemoglobin (Fe3+) competes with cytpchrome aa3 (Fe3+) for CN- forming a

methemoglobin-CN- complex

oxidative phosphorylation

mitochondrial electron transfer is linked to the generation of large amount of free energy, which is conserved in the form of the phosphate-bond energy of ATP;

An electrochemical gradient (protons, H+) is established by pumping H+ from the mitochondrial matrix to the

intermembrane space; the eletrochemical gradient is dissipated by coupling it to the synthesis of ATP by ATP synthase or Complex V or mitochondrial F1F0- ATPase

ATP synthase works together with a ____ _____ to aid the synthesis of ATP from ADP

phosphate carrier

Complex V include two components:

F1 and F0

F1 or coupling factor 1 or ATP-synthesizing unit,

that catalyzes the synthesis of ATP. this unit consists of five kinds of polypeptide chains (a, B,y, d, e)

F0 or proton conducting unit

whose role is to conduct protons. F0 is a hydrophobic segment that spans the inner mitochondrial membrane

stalk

between F0 and F1 unit contains several other proteins, one of them renders the complex sensitive to oligomycin

oligomycin

An antibiotic that blocks ATP synthesis by interfering with the utilization of the H+ gradient

the stalk is located in the

inner membrane

oligomycin

is an inhibitor of F1,F0-ATPase stops ATP synthesis and because the latter is coupled to electron flow (respiration), it also stops respiration

An ____ of respiration and phosphorylation dissipates the H+ gradient by transporting H+ from the intermembrane space to the matrix

uncoupler