146: ACETATE PATHWAY

resembles a phosphatidylcholine

functions at nanomolar concentrations, activates blood platelets, and contributes to diverse biological effects, including thrombosis, inflammatory reactions, allergies, and tissue rejection

platelet-activating factor

How many subunits do plants and bacteria have in their FAS? Note that it has 7 different enzymes with seven functionalities.

2

The central functionality of FAS

ACP

What is the configuration of unsaturated FA?

cis

Where does LCFUFA synthesis occur?

SER

essential FAs example

linoleic and linolenic acid

precursor of PG 1 series

dihomo-y-linolenic acid

precursor of PG 2 series

arachidonic acid

precursor of PG 3 series

eicosapentaenoic acid

rapeseed oil

erucic acid

Palm kernel and coconut oils

lauric acid

cod liver oil

eicosapentaenoic acid (EPA) (20:5) and docosahexaenoic acid (DHA) (22:6)

T/F: Most eukaryotic organisms possess a 9-desaturase enzyme that introduces a cis double bond into a saturated fatty acid, requiring O2 and NADPH or NADH cofactors.

True

T/F: Animals introduce new double bonds towards the carboxyl group. They also lack the 12 and 15 desaturase enzymes, so, although linoleic acid and α-linolenic acid are necessary for the synthesis of polyunsaturated acids that lead to prostaglandins and leukotrienes, animals must obtain these materials in the diet, mainly from plants.

True

leucine

isovaleryl-CoA

isoleucine

2-methylbutyryl-CoA

valine

isobutyryl

iterative and non-iterative

ACP dependent

bacteria and fungi

reduction may vary

PKS I

usual starter unit of PKS I

acetyl-CoA or propionyl-CoA

usual extender unit of PKS I

malonyl-CoA or methylmalonyl-CoA

iterative

ACP dependent

bacteria only

nonreducing

PKS II

T/F: starter unit of PKS II may vary

True

extender unit of PKS II

malonyl-CoA

iterative

ACP independent

plants, bacteria, and fungi

non reducing

PKS III

T/F: PKS III’s starter unit may come from other pathway (e.g., synthesis of flavonoids)

True

Examples of PKS I mediated

• erythromycin

• amphotericin B

• Lovastatin

• Rifamycin

T/F: Cyclicization occurs in PKS

True

condensation between alcohol and aldehyde

hemiacetal

condensation between alcohol and ketone

hemiketal

How do PKS III differ from other PKS?

uses CoA instead of ACP

What is the distinctive feature of aromatic system derived from PKS?

several of the carbonyl oxygens of the poly-β-keto system are retained in the final product. Meta oxygenated

T/F: Cyclization in PKS I often involved lactone or amide formation.

True

What’s unique with lovastatin synthesis?

Methylation is incorporated in PKS

What’s unique with rifamycin synthesis? and why it is considered as PKS I mediated even though the starting unit came from shikimate pathway, a characteristics commonly found in PKS III mediated compounds?

Starting unit is from shikimate pathway. Even though this is the case, it cannot be considered as PKS III because this synthesis involved ACP as well as the polyketide form prior to cyclization is partially reduced, unlike in PKS III, the polyketide is nonreduced.