Nucleotide metabolism Chapter 10

Function of neucleotides  Precursors for RNA and DNA synthesis  Energy substance in body (ATP)  Physiological Mediators (cAMP)  Components of coenzymes (NAD + ) Components of coenzymes (NAD + )  Allosteric effectors and donor of phosphate group (phosphorylation)  Formation of activated intermediates UDP-glucose, CDP-choline

Section 10.2 Nucleotide Synthesis and Degradation

Digestion and absorption of nucleotide Nucleoprotein ProteinNucleic acid Nucleases Nucleotide Nucleotidase PhosphateNucleoside Nucleosidase Base Ribose Absorption Blood

Metabolism of Purine nucleotides  Biosynthesis of purine nucleotides de novo synthesis 从头合成 salvage pathway 补救合成 GMPAMP

1.De novo synthesis of purine nucleotides CO 2 Glycine One carbon unit Glutamine Aspartate

 Characteristics of de novo synthesis of purine nucleotides 1. in cytosol 2. form IMP first, then synthesize AMP and GMP from IMP. 3. formation of purines is based on the ribosyl group of 5’-phosphoribose

R-5-P （ 5’-phosphoribose ） ATPAMP PRPPK Gly, one carbon units, Gln, CO 2, Asp involved step by step IMP AMP GMP H 2 N-1-R-5´-P （ 5´-phosphoribosyl-amine ） Gln Glu Glutamine PRPP amidotransferase (GPRT) PP-1-R-5-P （ 5’- phosphoribose 1’- pyrophosphate, PRPP ） 磷酸核糖焦磷酸

Regulation of de novo synthesis of purine nucleotides PRPPK PRPP GPAT PRA IMP Adenyl- succinate AMP ADPATP XMP GMP GDP GTP + + _ _ _ _ _ IMP Adenyl- succinate XMP AMPADP ATP GMPGDP GTP ATP GTP _ _ + + R-5-P ATP

2. Salvage synthesis of purine nucleotides  Material: PRPP, purine (conjunction) nucleosides (phosphorylation)  Location: brain and bone marrow or

adenine + PRPP AMP + PPi APRT hypoxanthine + PRPP IMP + PPi HGPRT guanine + PRPP HGPRT GMP + PPi adenosine Adenylate kinase ATPADP AMP APRT : adenine phosphoribosyltransferase HGPRT : hypoxanthine-guanine phosphoribosyltransferase

Degradation of purine nucleotides nucleotide nucleosides ribose-1-phosphate purine salvage pathway uric acid Nucleotidase Nucleoside phosphorylase 尿酸

IMP Neucleo -tidase Excretion

Metabolism of pyrimidine nucleotides  Biosynthesis of pyrimidine nucleotides de novo synthesis salvage pathway

1.De novo synthesis of pyrimidine nucleotides Aspartate Glutamine CO

 Characteristics of de novo synthesis of pyrimidine nucleotides 1. mostly in cytosol 2. form UMP first, then synthesize other pyrimidine nucleotides from UMP. 3. in the synthesis of UMP, pyrimidine ring is formed first, then combined with PRPP.

Process of de novo synthesis of UMP  1. formation of Carbamoyl phsphate (CP) CO 2 + glutamine + H 2 O + 2ATP C O H2NH2N O ~ PO ADP + Pi carbamoyl phosphate Carbamoyl phosphate synthase Ⅱ (CPS Ⅱ )

The different between Carbamoyl phosphate synthase Ⅰ, Ⅱ Location Source of nitrogen Activator Function NH 3 Glutamine NoneN-acetylglutamate Mitochondria of liver cells cytosol of all cells Formation of urea Formation of pyrimidine

C O H2NH2N O ~ PO 3 2- carbamoyl phosphate + Aspartate Carbamoyl aspartate PRPP Orotate 乳清酸 UMP 2. Formation of UMP

ATPADP UMPK UDP NDK ATPADP UTP CTP synthase Gln ATP Glu ADP 3. Synthesis of CTP, dTMP or TMP dCMP dUDP dUMP dTMP TMP synthase

Regulation of de novo synthesis of pyrimidine nucleotides ATP + CO 2 + glutamine Carbamoyl phosphate UMP Carbamoyl aspartate UTP CTP aspartate ATP + 5-phosphate ribose PRPP Pyrimidine nucleotides Purine nucleotides Activated by substrates 2.Inhibited by products

Salvage pathway of pyrimidine nucleotides Uracil + PRPP UMP + PPi Uracil phosphate ribosyltransferase Uridine + ATP Uridine kinase UMP +ADP Uracil + 1-phosphoribose Uridine + Pi Uridine phosphorylase

nucleotide nucleosides phosphoribose pyrimidine Degradation of pyrimidine nucleotides Nucleotidase Nucleoside phosphorylase

Cytosine NH 3 Uracil dihydrouracil H 2 O CO 2 + NH 3 β-alanine Thymine β-ureidoisobutyrate H2OH2O Acetyl CoA TAC liver Urea ++ β-aminoisobutyrate Succinyl CoA TAC Glucose Excreted in urine

Deoxyribonucleotide biosynthesis NDP dNDP Ribonucleotide reductase dNDP + ATP kinase dNTP + ADP

Biosynthesis of NDP and NTP AMPADPATP ADPATP Kinase ADPATP Kinase XMP XDP XTP YDPYTP Kinase YDPYTP Kinase

Section 10.3 Dysmetabolism of nucleotides and antimetabolites

Dysmetabolism of nucleotides  Caused by the genetic defect or regulatory abnormality of some enzymes participating nucleotide metabolism. Gout （痛风）： pain and tenderness, redness, heat, swelling and joint inflammation Causes ： too much uric acid forms crystals in joints and cause inflammation

Risk Factors  Obesity/being overweight Obesity  more common in men than women  Certain medicines  Certain foods and alcoholic beverages  Genetics  Enzyme defect Enzyme defect

Medication  xanthine-oxidase inhibitors, 黄嘌呤氧 化酶抑制剂 allopurinol 别嘌呤醇allopurinol  uricosurics, 促尿酸尿剂 uricosurics  urate oxidases 尿酸氧化酶urate oxidases

 Limit your consumption of certain types of meat ： beef, pork, lamb, and “organ meats” (such as liver, kidney, and brain), as well as meat extracts and gravies.  Reduce or eliminate alcohol consumption, especially beer.  Reduce your use of oatmeal, dried beans, spinach, asparagus, cauliflower, and mushrooms  High consumption of seafood is associated with an increased risk of gout.

Antimetabolites  The analogs of ribonucleotide metabolite intermediates synthesized artificially.  Can interfere, inhibit and block the ribonucleotide metabolism.  Used as drugs.

 Purine ribonucleotide metabolite analogs 6-mercaptopurine(6-MP ) Hypoxanthine (6-MP)

 Pyrimidine ribonucleotide metabolite analogs : 5-fluorouracil(5-FU), (T)(5-FU)

NAD + AMP

Biological oxidation  Respiratory Chain and its composition ， How many Respiratory Chain in the mitochondria? What is the sequence of them?  Oxidation Phosphorylation and the mechanism of it  the regulation of it (Cyanide)?  P/O ratio  How many ATP produced by Respiratory Chain? How to use cytosolic NADH ?  energy-rich compounts

Protein catabolism  Nitrogen Balance, Essential Amino Acids, Complementary effect, Putrefaction, Amino acid metabolic pool, Ketogenic amino acids, Ketogenic and glucogenic amino acids.  deamination, decarboxylation key enzymes, main pathway, main products

 ALT, AST (function)  SAM, PAPS, GSH, Dopamine, creatine phosphate (function, formation)  Ammonia, One Carbon Units carrier, source, utilization  Hyperammonemia, PKU, Albinism damage, mechanism

Nucleotide metabolism  Function of neucleotides  de novo synthesis of purine and pyrimidine nucleotides material, character, main steps,  Salvage pathway of purine and pyrimidine  Degradation of purine and pyrimidine nucleotides products ， Gout  Deoxyribonucleotide biosynthesis