Biochemistry

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Refers to a natural process converting atmospheric nitrogen to ammonium to yield usable nitrogen source. • Only a few prokaryotic species can "fix" nitrogen. • Nitrogenase complex dinitrogenase dinitrogenase reductase

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Nội dung Text: Biochemistry

Subject: Biochemistry Instructor: MSc. Le Hong Phu Day: 2 P eriod: 1234 Semester 2 Academic year: 2009-2010 Group 4
GROUP MEMBERS Nguyễn Thị Thúy Giang BTIU08047 Chung Thế Hào BTUN08015 Lại Nguyên Huy BTIU08015 Nguyễn Quang Huy BTWE08012 Đặng Xuân Khải BTIU08019 Dương Bá Phú BTIU08058 Trần Triệu Quân BTUN08027 Đường Thị Kiều Trang BTWE08 Huỳnh Hải Vân BTIU08
OUTLINE I. Introduction II. Body 1. Nitrogen fixation 2. Transamination reaction and incorporation of ammonium 3. Biosynthesis of amino acids i. Glutamate ii. Aspartate iii. Serine iv. Pyruvate v. Aromatic vi. Histidine
4. One carbon metabolism 5. Amino acids as metabolic precursor i. Glutathione ii. Alkaloid iii. Nucleotides iv. Heme group 6. Regulation of amino acid biosynthesis III. Conclusion
INTRODUCTION WHY CARES? Nitrogenous compounds are prevalent. Nitrogenous compounds are metabolic important  Determine our health. Human alone cannot synthesize all these compounds
WHAT WE FOCUS? The “build up” of nitrogenous compounds (monomer only): amino acids and more. Only some forms of nitrogen are accessible The biosynthesis pathways are extensively diverse. Nitrogen balance: Positive: intake > loss  childhood, pregnancy, illness recovery. Negative : intake < loss  Malnutrition. Neutral: intake = loss  adulthood.
NITROGEN FIXATION • Refers to a natural process converting atmospheric nitrogen to ammonium to yield usable nitrogen source. • Only a few prokaryotic species can "fix" nitrogen. • Nitrogenase complex dinitrogenase dinitrogenase reductase
Dinitrogenase: – Referred to as Fe-Mo protein. – Heterotetramerous, containing two Mo atoms, and 30 iron atoms. – Catalyze the reaction: N2 + 8H+ + 8e-  2NH3 + H2 Dinitrogenase reductase: – Referred to as Fe protein. – is a dimer – Carry electrons from ferrodoxin and integrate with ATPs.
16 ATPs are spent to reduce a N2 to 2 NH3  expensive
TRANSAMINATION • Reaction involving transferring an α amino group from an α amino acid and an α keto acid. • 2 typical α-keto acids : α-ketoglutarate, pyruvate (carbonyl group is directly adjacent to carboxyl group). O H O H O O O O + R2 O- + C C O→ - - C C R1 C O C R2 O- C C ←R1 NH3+ NH3+ Donor amino acid New keto acid New amino Acceptor acid keto acid REVERSIBLE
• Transamination occurs in eukaryotic cells (aminotransferases) and can be found in cytoplasm or mitochondria. • Aminotransferase possesses 2 types of specificity: – α-amino acid donate α-amino group. – α-keto acid accept α-amino group.
• Most of aminotransferases use glutamate as amino group donor. • Glutamate is produced when α-ketoglutarate accept an amino acid group. α-ketoglutarate and glutamate pair play an important role in metabolism of amino acid.
Vitamin B6 is a cofactor of aminotransferases
H H N+ HHO C Enzyme O + OH R C C C O- αβ O- P O H NH3+ O- N+ CH 3 α-amino acid H H2O ↑↓ Pyridoxal phosphate H2O H HO R C C C O- βα H N+ HC H O O- O- P O Schiff base O- N+ C H3 H H+ ↑↓ H +
H O H O C C O- RC C C O- RC H N+ H N+ HC H O ↔ HC H O O- O- - O P O O- P O Quinonoid O- O- N + CH3 N CH3 Carbanion H H ↑↓ H+ H+ H O C C O- RC H N+ H 2C H O O- - O P O O- N+ CH3 H H2O NH2 H2O ↑↓ H2C O HOO O- Pyridoxamine - O C O- P O RCC α-keto acid + phosphate H O- N+ CH3 H
DIRECT INCOPORATION OF AMMONIUM 2 means of NH4+ incorporation into amino acid Reductive amination of α-keto acid. Glutamate dehydrogenase Catabolic function: prepare ammonium for excretion. Reversible  when ammonia , glutamate synthesis Present in mitochondria and cytoplasm
Formation of amide from aspartate or glutamate, forming asparigine and glutamine Glutamate synthase Excessive ammonium is dangerous to brain  converted to glutamine and transported to the liver.
• In plants, incorporation require 2 enzymes: – Glutamine synthase – Glutamate synthase NH4+ incorporate to glutamine by glutamine synthase, amide nitrogen is transferred to 2-keto group of α-keto glutarate by glutamate synthase.
BIOSYNTHESIS OF AMINO ACIDS Amino Acid Protein building blocks Carbon skeleton can be used as source for energy. Precursors for nucleotide and lipid biosynthesis. Essential versus Non-essential amino acids Arginine and Histidine can be essential in some certain case