Nitrogen metabolism
Download
1 / 24

Nitrogen Metabolism - PowerPoint PPT Presentation


  • 103 Views
  • Uploaded on

Nitrogen Metabolism. Protein degradation and turnover Amino acid degradation and urea cycle Nitrogen cycle Nitrogen fixation Amino acid biosynthesis Amino acid derivatives. How Much Protein?. A 70 kg person (154 lb) typically consumes 100 g protein per day

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Nitrogen Metabolism' - lenore-holder


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Nitrogen metabolism
Nitrogen Metabolism

  • Protein degradation and turnover

  • Amino acid degradation and urea cycle

  • Nitrogen cycle

  • Nitrogen fixation

  • Amino acid biosynthesis

  • Amino acid derivatives


How much protein
How Much Protein?

  • A 70 kg person (154 lb) typically consumes 100 g protein per day

  • To stay in nitrogen balance that person must excrete 100 g of N products per day

  • The body makes 400 g of protein per day and 400 g are broken down

  • 300 g of amino acids recycled into new protein, 100 g are degraded

  • Total protein = 500 g/day, 400 g degraded, 400 resynthesized and 100 g catabolized


Characteristic of proteins in cells
Characteristic of Proteins in Cells

  • Synthesized and degraded constantly -Turnover

  • Turnover may be minutes, weeks or longer

  • Synthesis requires essential and non essential amino acids

  • Degradation is programmed and regulated

  • Control point enzymes most labile; constitutive most stable

  • Nutritional state and hormones affect degradation rates (glucocorticoids, insulin, etc.)


The half life of proteins is determined by rates of synthesis and degradation

dC

Rate of Turnover =

= KS - KDC

dt

The half-life of proteins is determined by rates of synthesis and degradation

A given protein is synthesized at a constant rate KS

A constant fraction of active molecules are destroyed per unit time

KS is the rate constant for protein synthesis; will

vary depending on the particular protein

C is the amount of Protein at any time

KD is the first order rate constant of enzyme degradation,

i.e., the fraction destroyed per unit time, also

depends on the particular protein


dC

= 0

dt

Steady-state is achieved when the amount of protein

synthesized per unit time equals the amount being destroyed

0.693

KDC = KS

t 1/2 =

KD

C

Protein

concentration

(enzyme activity)

Stop protein synthesis,

measure rate of decay

Hours after stopping synthesis


Steps in Protein Degradation

ATP

AMP + PPi

Transformation to a degradable form

(Metal oxidized, Ubiquination, N-terminal residues, PEST sequences)

Lysosomal Digestion

26S Proteasome digestion

7  type, 7  type

subunits

Proteolysis to peptides

KFERQ

8 residue fragments

Ubiquination

N-end rule: DRLKF: 2-3 min

AGMSV: > 20 hr

PEST: Rapid degradation


Glycine at C terminal of Ubiquitin

Ubiquitin

COO-

Ubiquitin activating enzyme

ATP

E1

HS

Ubiquitin conjugating enzyme

20 or more per cell

AMP + PPi

O

C

S

E1

3

E2

SH

NH3+

N

HS

E2

HS

E1

NH3+

N

H3N+

O

3

C

S

E2

N

O

O

O

O

ATP

C

C

C

C

NH

Ubiquitin-

specific proteases

(26S proteasome)

E3

AMP + PPi

Poly Ubiquitin

Degraded

protein

+ Ubiquitin

Activation

of Ubiquitin

Ubiquitin

ligase

Ubiquination

Page 1075


Cervical Cancer

Human Papilloma virus (HPV)

Activates the E3 that catalyzes ubiquination of p53 tumor suppressor and DNA repair enzymes (occurs in 90% of cervical cancers)

Mutated DNA is unchecked and allowed to replicate

P472


19S

20S

Catalysis

in beta

19S

7 alpha

7 beta

Subunits

26S Proteasome

(2000 kD)

Opening for ubiquinated protein to enter

8-residue peptides diffuse out


Amino Acids

Amine Group

Carbon Skeleton

Glutamate

Biosynthesis

Degradation

Amino Acids

CO2 + H2O

Urea

Amino Acid

Derivatives


COO-

Amine group acceptor

COO-

+

H3N-C-H

C=O

CH2

CH2

CH2

CH2

COO-

Amine group donor

COO-

-Ketoglutarate-Glutamate

-Kg

L-glutamate

AA1 + -KG

-ketoacid + glutamate

acceptor

donor

Amino transferases

Requires pyridoxal-5’-phosphate


CH2OH

CH2NH2

O

HO

HO

C

CH2OH

CH2OP

H

HO

CH2OP

H3C

H3C

N

N

H3C

N

Vitamin B6

Pyridoxine

Cofactor (N acceptor)

Pyridoxal-5’-PO4

Cofactor (N donor)

Pyridoxamine-PO4


COO-

COO-

COO-

+

H3N-C-H

+

COO-

C=O

H3N-C-H

CH2

C=O

CH2

CH3

CH2NH2

CH2

CH3

O

O

CH2

HO

COO-

C

C

CH2OP

COO-

H

H

HO

HO

CH2OP

CH2OP

H3C

N

H3C

H3C

N

N

Alanine-Pyruvate Aminotransferase

+

+

forward

reverse


Mechanism

Alanine

Glutamate

-Ketoglutarate

Pyruvate

In

Out

In

Out

Enz-CHO

(E-B6-al)

Enz-NH2

(E-B6-am)

Enz-NH2

Enz-CHO

Ordered Ping-Pong Mechanism


COO-

COO-

+

H3N-C-H

C=O

CH2

CH2

CH2

CH2

COO-

COO-

Forward Reaction

Reverse Reaction

Glutamate Metabolism

+ NAD(P)+

+ H2O

+ NAD(P)H + H+

Glutamate

dehydrogenase

+ NH4+

Urea cycle

specific for glutamate

specific for -ketoglutarate

requires NAD+

requires NADPH

delivers NH4+ to urea cycle

Fixes NH4+, prevents toxicity


COO-

COO-

COO-

COO-

+

+

+

+

H3N-C-H

H3N-C-H

H3N-C-H

H3N-C-H

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

COO-

COO-

C=O

C=O

NH2

OPO3=

Glutamate-PO4

intermediate

Urea

Glutamine Metabolism

+ ATP + NH4+

+ ADP + Pi

Glutamine

Synthetase

L-glutamine

H2O

Glutaminase

+ NH4+


glutamine

Overall Scheme Using Alanine as an Example

Amino transferase with pyridoxal-5’-PO4

Alanine

Pyruvate

-ketoglutarate

glutamate

Glutamate dehydrogenase

with NAD+

Glutaminase with H2O

NH4+

Urea

Glutamate and glutamine are the only donors

of NH3 to the Urea Cycle


The urea cycle
The Urea Cycle

1. Occurs in the liver mitochondria and cytosol

2. Starts with carbamoyl-PO4

3. Ends with arginine

4. Requires aspartate

5. Requires 3 ATPs to make one urea


O

O

~

O-P-O

H2N

C

O

High energy bond

Synthesis of Carbamoyl-PO4

NH4+ + HCO3- + 2 ATP

+ 2 ADP + Pi

Carbamoyl phosphate Synthetase I


NH2

+

+

NH

NH3

H2N=C

CH2

CH2

CH2

CH2

CH2

CH2

H

H

O

C

C

COO-

COO-

H3N

H3N

NH2

H2N

Citrulline

Aspartate

Carbamoyl-PO4

ATP

Urea

Cycle

Ornithine

Argininosuccinate

Arginine

H2O

C

Urea


Reactions of Urea Cycle

O

COO-

C

COO-

H2N

OPO3

H3N+-C-H

H3N+-C-H

CH2

CH2

+

+ OPO3=

CH2

CH2

CH2

Carbamoyl-PO4

CH2

NH

Citruline

+

NH3

O=C

Ornithine

NH2

COO-

COO-

H3N+-C-H

H3N+-C-H

COO-

ATP

ADP + Pi

CH2

CH2

CH2

+

H-C-NH3

+

CH2

CH2

CH2

CH2

COO-

COO-

NH

NH

CH2

L-Aspartate

O=C

=C

H-C-N

NH2

NH2

Argininosuccinate

COO-

Cytosol

Mitochondria


COO-

C

H

H

C

H2N+

COO-

COO-

COO-

H3N+-C-H

H3N+-C-H

COO-

COO-

COO-

CH2

CH2

CH2

CH2

CH2

+

H-C-NH3

CH2

CH2

H

C=O

C-OH

CH2

CH2

COO-

COO-

COO-

COO-

NH

NH

CH2

=C

=C

H-C-N

NH2

NH2

COO-

Cytosol

+

Fumarate

L-Arginine

L-Malate

L-Aspartate

Oxaloacetate


O

C

H2N

NH2

H2N+

COO-

H3N+-C-H

CH2

CH2

CH2

NH

=C

NH2

COO-

H3N+-C-H

CH2

H2O

CH2

+

CH2

NH3

+

Urea

Ornithine

L-Arginine

Return to Mitochondria


ad