CARNITINE

Gamma-hydroxi-N-trimethylamino-butyrate

Sources of blood carnitine: a.) mainly animal source food: 1-8 %, 300 μmole/day

b.) we synthesize in liver (brain, kidney): 1-2%, 100 μmoles/day

c.) in kidney absorbed from the filtrate to the blood: 92-98% (most important)

Excretion- by urine 400 μmoles/day

-through gut: changable amount

Tissue contentblood plasm 300 μmoles/5 liters, 40-60 μmoles/L

skeletal muscle 2000-3000 μmoles/kg

liver, heart 800-1500 μmoles/kg

other tissues 600-700 μM

all carnitine in tissues 50000 μmoles

Carnitine concentration is bigger in every cells than in blood, therefore the

entrance is always active transport, the departure is passive.

Carnitine is ionic (zwitter ion), so it requires in every membrane (plasma, mitochondria,

ER) a protein transporter.

Synthesis

Last step is only in liver (brain and kidney insufficient amount).

Starts from proteins, on Lys

Localization of steps one after each other: nucleus, lysosome, mitochondria,

cytoplasm

Requires: SAM (Met), Lys, ascorbate, PLP, NAD, enzymes

a) Vitamin or enzyme deficiency leads to improper synthesis, but food carnitine

is enough.

b) Strict vegetarian people can not eat high amount, but absorption from gut becomes

more efficient.

c) When carnitine transporter in the kidney does not function, carnitine is exreted by

the urine, causing systemic carnitine deficiency in all the body.

Lys és Met: essencial amino acids

B6-vitamin l

the last step is sufficient only in liversmall amount in brain,kidney

ascorbate

B3-vitamin

Carnitine transporters in the membranes

1.) OCTN2 = organic cation transporter(uniporter) =

high affinity carnitine/Na+ symporter Kt = 1-6 microM

carnitine reabsorption from the filtrate to the blood in the apical

tubular cells in kidney

carnitine entrance from blood to cells: skel. mucle, heart, pancreas,

placenta, brain, lung, testis, fibroblast

OCTN2 transporter protein hereditary deficiency leads to systemic

carnitine deficiency

2.) OCTN3 = intermediate affinity carnitine specific uniporter Kt= 20 μM

spermium, liver peroxisome

3.) OCT 1,2,3 = intermediate affinity organic cation uniporters or

exchangers

basal membrane of tubular cells in kidney, intestine, muscle, testis

4.) OCTN1 = low affinity organic cation/ H+ antiporter Kt > 500 μM

in kidney proximal tubules acyl-carnitines: alkaloids, medicines etc. are

exreted to filtrate

lung, bone marrow, prostate, placenta, pancreas, heart,

uterus, spleen, testis...

in mitochondrial inner membrane

5.) ATBo,+ is a basic amino acid uniporter Kt = 0.8 mM

lung, intestine, mammary gland

6.) small affinity carnitine/Na+ symporter = high affinity gamma-butyrobetain/Na+

symporter in liver, brain

Carnitine is synthesized from gamma-butyrobetain in one step.

= OCTN1

acyl-carnitine

carnitine

Function of carnitine

1.) Entrance of LCFA (long chain fatty acids) to mitochondria, ER, peroxisome

2.) Leaving of SC(F)A short chain acids from cell organells and cells to excrete out

of the cells and the body (as acyl-carnitine).

In case of OCTN2 hereditary deficiency carnitine can not be reabsorbed from

filtrate, rather it is flowed out of the body, causing systemic deficiency.

Function of carnitine: to transport fatty acids into and out of cell organells

VLC = very long chainCAC = carnitine/acyl-carnitine translocase

c) No enough acetyl-CoA for citric acid cycle and activation of pyruvate carboxylase,

gluconeogenesis does not proceed, glucose is not replenished.

d) In starvation in liver no ketone body synthesis (from FA derived acetyl-CoA),

so the brain can not gain them instead of glucose.

e) Heart always oxidizes FAs, skeletal muscle uses FAs in resting and long term

exercise. Without FA beta-oxidation no enough ATP for movement,

causing tiredness, heart hyperthrophy, progressing cardiomyopathy,

death of 2-4 years old child

f) FAs can not enter to cell organells, they are accumulated in cytoplasm activating

TAG synthesizing enzymes, causing lipid degeneration in liver, heart,

muscle

Never nowhere fatty acids can enter to mitochondria to be oxidized, therefore:

a) always everywhere glucose (and amino acids) are degraded to yield energy,

glucose is consumed very fast, causing between meals life threatening

hypoglycemia, coma

b) in liver, muscle etc. PDHC is not inhibited by acetyl-CoA (from FA oxidation)

during fasting, glucose is not spared for obligate glucose consuming

tissues

Signs of systemic carnitine deficiency

Therapy

Big dose of oral carnitine during the whole life for little affinity carnitine transporters

to work.

5% of normal concentration in cells is enough.