BCM6221 Synthesis of Fatty Acids, Complex Lipids, and Eicosanoids

acyl carrier proteins

Intermediates in synthesis are linked to -SH groups of?

CoA

Intermediates in oxidation are linked to -SH groups of?

Cytosol

Where does fatty acid synthesis occur?

Mitochondria

Where does fatty acid breakdown occur?

fatty acid synthase

Enzymes of fatty acid synthesis are one polypeptide namely?

False. Fatty acid biosynthesis uses NADPH/NADP+ while fatty acid breakdown uses NADH/NAD+.

Fatty acid biosynthesis uses NADH/NAD+ while fatty acid breakdown uses NADPH/NADP+.

T or F?

acetyl-CoA

Fatty acid chains are constructed by the addition of two-carbon units derived from?

malonyl-CoA

The acetate units are activated by carboxylation with CO2 to form ______ at the expense of ATP.

decarboxylation

The addition of two-carbon units to the growing chain is driven by _______ of malonyl-CoA.

palmitic acid

The elongation reactions are repeated until the growing chain reaches 16 carbons in length which is also known as?

Carboxylation of acetyl-CoA to form malonyl-CoA

What is the irreversible, committed step in fatty acid biosynthesis?

Acetyl-CoA carboxylase

Carboxylation of acetyl-CoA to form malonyl-CoA is catalyzed by which enzyme?

1. bicarbonate
2. ATP
3. biotin

Acetyl-CoA carboxylase uses these 3 cofactors:

3 subunits

E. coli ACC has how many subunits?

1. biotin carboxyl carrier protein
2. biotin carboxylase
3. carboxyltransferase

Animal ACC is one polypeptide with inactive protomers containing all three functions namely:

N-carboxybiotin

Bicarbonate is activated for carboxylation reactions by formation of?

carbonylphosphate intermediate

ATP drives the carboxylation of biotin forward, with the transient formation of what intermediate?

transcarboxylation

In a typical biotin-dependent reaction, nucleophilic attack by the acetyl-CoA carbanion on the carboxyl carbon of N-carboxybiotin -- a ______ reaction -- yields the carboxylated product.

carbonyl-phosphate

In the ACC reaction, the biotin ring acquires carbonyl groups from ____ on the biotin carboxylase subunit.

carboxyltransferase

Biotin on a flexible tether delivers carboxyl groups from the carboxylase to the?

Acetyl-CoA carboxylase (ACC)

In animals, this enzyme is a long, active filamentous polymer formed from inactive protomers.

True.

As a committed step, ACC is carefully regulated.

T or F?

False. Monomers.

Palmitoyl-CoA favors dimers.

T or F?

False. Active polymeric form.

Citrate favors the inactive, polymeric form of ACC.

T or F?

Phosphorylation

This reaction modulates citrate activation and palmitoyl-CoA inhibition.

phosphorylation state

The regulatory effects of citrate and palmitoyl-CoA are dependent on the __________ of ACC.

8 to 10 sites

The animal ACC enzyme is phosphorylated at __ to __ sites on each enzyme subunit.

citrate; low [citrate]

Unphosphorylated E has high affinity for ____ and is active at _____.

palmitoyl-CoA; high [palmitoyl-CoA]

Unphosphorylated E has high Ki for ______ and _____ is required to inhibit.

citrate; high [citrate]

Phosphorylated E has low affinity for _____ and ____ is needed to activate.

palmitoyl-CoA; low [palmitoyl-CoA0

Phosphorylated E has low Ki for ________ and is inhibited at ________.

Acyl carrier protiens (ACP)

This is the carrier of intermediates in fatty acid synthesis; a large "CoA".

sulhydryl group

Fatty acids are conjugated both to coenzyme A and to acyl carrier protein through the ______ group of phosphopantetheine prosthetic groups.

fatty acyl synthase I (FAS I)

Fatty acid synthesis in mammals occurs on homodimeric ________, which consists of 270-kD polypeptides which contain all the reaction centers required to produce a fatty acid.

yeast and fungi (lower eukaryotes)

In ____, the activities of FAS are distributed on two multifunctional polypeptide chains.

fatty acid synthase II (FAS II)

In plants and bacteria, the enzymes of FAS are separate and independent, and this collection of enzymes is referred to as?

6

The mammalian pathway is a cycle of elongation that involves how many enzyme activities?

malonyl-CoA-acetyl-CoA-ACP transacylase (MAT)

Elongation is initiated by transfer of the acyl moiety of acetyl-CoA to the acyl carrier protein by what enzyme?

This enzyme also transfers the malonyl group of malonyl-CoA to ACP.

ACP conjugates

Acetyl and malonyl building blocks are introduced as?

Decarboxylation

This reaction drives the beta-ketoacyl-ACP-synthase reaction and results in the addition of two-carbon units to the growing chain.

MAT, acyl carrier protein, ketoacyl synthase

An acetyl group is transferred from CoA to ____, then to the ____. and then to the ______.

MAT, acyl carrier protein

A malonyl group is transferred to ____ and then to the ____. C-C bond formation follows.

True.

Fungal fatty acid synthase is a closed barrell.

T or F?

asymmetric X-shaped structure

Mammalian fatty acid synthase is an _______ structure.

mitochondria and ER

C16 fatty acids may undergo additional elongation in both the?

O2-independent process

Introduction of cis double bonds in prokaryotes use a/an O2-(independent, dependent) process.

O2-dependent process

Introduction of cis double bonds in eukaryotes use a/an O2-(independent, dependent) process.

thioester

E. coli adds double bonds while the site of attack is still near a functional group which is the?

True.

Eukaryotes add double bond to the middle of the chain and need the power of O2 to do it.

T or F?

dehydrases

Double bonds are introduced into the growing fatty acid chain in E. coli by specific _______.

Palmitoleoyl-ACP

This is synthesized by a sequence of reactions involving four rounds of chain elongation, followed by double bond insertion by beta-hydroxydecanoyl thioester dehydrase and three additional elongation steps.

cis-vaccenoyl-ACP

Another elongation cycle, produces cis-vaccenic acid as?

stearoyl-CoA desaturase

The conversion of stearoyl-CoA to oleoyl-CoA in eukaryotes is catalyzed by _______ in a reaction sequence that also involves cyt b5 and cyt b5 reductase.

linoleic acid

Arachidonic acid is synthesized from ___ in eukaryotes. This is the means by which animals synthesize fatty acids with double bonds at positions other than C9.

essential fatty acids

Linoleic acid and linolenic acid are termed (non-essential, essential) fatty acids because animals cannot synthesize them and must acquire them in their diet.

Linoleic acid

This is the precursor of arachidonic acid and both these are termed as omega-6 fatty acids.

Linolenic acid

This is the precursor of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and these three are termed omega-3 fatty acids.

omega-3

(omega-6, omega-3) fatty acids are cardioprotective, anti-inflammatory, and anticarcinogenic.

omega-6

(omega-6, omega-3) fatty acids are precursors of prostaglandins, thromboxanes, and leukotrienes.

Malonyl-CoA

This blocks the carnitine acyltransferase and thus inhibits beta-oxidation.

Citrate

This activates acetyl-CoA carboxylase.

Fatty acyl-CoAs

These inhibit acetyl-CoA carboxylase.

Glucagon

This activates lipases and inhibits ACC.

Insulin

This inhibits lipases and activates ACC.

False. Only in eukaryotes.

Sphingolipids and triacylglycerols are made in both eukaryotes and prokaryotes.

T or F?

Lipins

These are phosphatidic acid phosphates (PAPs) that are widely conserved in eukaryotes.

Critical for triacylglycerol biosynthesis and for maintenance of nuclear structure and organization of the ER membrane.

transmembrane domains

Lipins lack _____ domains and are extensively phosphorylated and confined to the cytosol until activated.

Nem1p and SPo7p

Lipin activation occurs upon PAP binding to a complex of two ER/nuclear transmembrane proteins namely ___ and ____, followed by dephosphorylation of PAP.

di- and triacylglycerols

The lipin-Nem1p-Spo7p complex dephosphorylates PA to form (2):

Phosphatidic acid

This is the precursor for all the other glycerolipids in eukaryotes; may be formed from dihydroxyacetone phosphate or glycerol.

1. diacylglycerol
2. cytidine diphosphate diacylglycerol

Phosphatidic acid is made either into (2):

CDP-diacylglycerol or diacylglycerol

Eukaryotes synthesize glycerolipids from _______ or _______, which are the principal precursors of glycerolipids in eukaryotes.

acyltransferases

Triacylglycerols are formed primarily by the action of these enzymes on monoacylglycerol and diacylglycerol.

phosphatidylinostil

CDP-diacylglycerol is used in eukaryotes to produce ____ in one step.

Phosphatidylglycerol

CDP-diacylglycerol is used in eukaryotes to produce ____ in two steps.

cardiolipin

CDP-diacylglycerol is used in eukaryotes to produce ____ in 3 steps.

Dihydroxyacetone phosphate

This is a precursor of the plasmalogens.

Acylation

____ of dihydroxyacetone phosphate, followed by an exchange reaction produces the ether linkage, then ketone reduction occurs.

CDP-ethanolamine

This delivers the head group.

desturase

This enzyme produces the double bond in the alkyl chain.

acetylation

Platelet-activating factor is formed by ______ of 1-alkyl-2-lyso-phosphatidyl-choline.

acetylhydrolase

Platelet-activating factor is degraded by the action of _____.

serine and palmitoyl-CoA

Sphingolipid biosynthesis begins with condensation of (2):

pyridoxal phosphate (PLP)

3-ketosphinganine synthase requires ______ as a coenzyme.

NADPH

Ketone is reduced with the help of _____, catalyzed by 3-ketosphinganine reductase.

double bond formation

Acylation is followed by ________.

Ceramide

This is the resulting product of sphingolipid biosynthesis which serves as a precursor for other sphingolipids and cerebrosides.

Eicosanoids

These are 20-carbon molecules which are ubiquitous breakdown products of phospholipids.

1. prostaglandins
2. thromboxanes
3. leukotrienes
4. other hydroxyeicosanoic acids

Eicosanoids are local hormones including (4):

arachidonate

Prostaglandins are formed from _______ by oxidation and cyclization.

prostaglandin endoperoxide H synthase (PGHS) a.k.a cycloxygenase (COX)

Biosynthesis of prostaglandins is initiated by an enzyme from the ER called?

1. cyclooxygenase (COX)
2. glutathione-dependent peroxidase (POX)

prostaglandin endoperoxide H synthase (PGHS) has 2 different activities namely:

Lipoxins

These are anti-inflammatory eicosanoids which are synthesized through the concerted actions of several lipoxygenases -- including 5-LO, 12-LO, and 15-LO.

transcellular biosynthesis

Lipoxins are products of ______, which expands the number of active mediators synthesized in response to stimuli.

Acetylalicylate (aspirin)

This drug inhibits the COX activity of endoperoxide synthase via acetylation (covalent modification) of Ser-530.

Prostaglandins

These are potent mediators of inflammation.

nonsteroidal anti-inflammatory drugs (NSAIDs)

PGHS/COX is inhibited by the ________.

isoleucine

COX-1 has a bulkier ____ at position 523 which prevents binding of COX-2 inhibitors.

valine

COX-2 has _____ at position 523 which accommodates the COX-2 inhibitors.

Aspirin and bromoaspirin

These 2 drugs binds covalently to COX-1 and -2.