Download presentation
Presentation is loading. Please wait.
Published byAlison Farmer Modified over 8 years ago
1
Vitamin B 12 Julie Roche
2
Vitamin B 12 Cobalamin Porphyrin ring Cobalt Nucleotide Net charge = +1
3
Vitamin B 12 Derivatives Cyanocobalamin (digested form) Hydroxycobalamin Chlorocobalamin Methylcobalamin Adenosylcobalamin (5’-deoxyadenosylcobalamin)
4
Back to Image Search <>
5
Biosynthesis of Vitamin B 12 One of the most complicated biosynthetic pathways Involves over 30 enzymes Two pathways Aerobic anaerobic 16 intermediates between uroporphyrinogen III and adenosylcobalamin (aerobic pathway)
7
Difference between pathways Need for molecular O 2 Aerobic: between precorrin-3a and b Point of Cobalt addition Anaerobic: added early, between uroporphyrinogen III and precorrin-2 Aerobic: added late, between hydrogenobyrinic acid a,c-diamide and cob(II)lyrinic acid a,c- diamide *Anaerobic synthesis is more difficult
8
Developments Leading to the Discovery of the Biosynthetic Pathway of Vitamin B 12 13 C labeling (1990) NMR spectroscopy Enzymology Molecular genetics
9
Vitamin B 12 Produced on an industrial level Fermentation –Methanosarcina –Butribacterium –Acetobacterium –Propionibacterium Produces largest amt of cobalamin Secretes propionic & acetic acid –Propionic acid inhibits cobalamin production
10
Vitamin B 12 affects two Major Pathways Homocysteine Methionine Methylmalonyl CoA Succinyl CoA
11
The effects of Vitamin B 12 on the conversion of homocysteine to methionine Homocysteine Methionine Methylcobalamin Methionine Synthase 5-methyltetrahydrofolate tetrahydrofolate Tetrahydrofolate methyltransferase
12
The effects of Vitamin B 12 on the conversion of Methylmalonyl CoA to Succinyl CoA Methylmalonyl Co A Succinyl CoA Adenosylcobalamin Methylmalonyl CoA mutase
13
Vitamin B 12 Deficiency homocysteine and methylmalonyl CoA Increase in methylmalonyl CoA –Increased enzyme activity in fatty acid synthesis Build up of odd fatty acids around peripheral nerves Increase in homocysteine –Vascular/nervous problems
14
Vitamin B 12 Deficiency Excess homocysteine & MMA excreted in urine –Diagnosis for cobalamin deficiency Methylmalonyl CoA mutase & Methionine synthase affect amino acid metabolism –Amino acid metabolism inhibited by deficiency
15
Vitamin B 12 Binding Proteins
16
Transcobalamin I R-type binding protein 33% is carbohydrate Molecular weight = 125,000-150,000 Beta globulin Contains more sialic acid than transcobalamin III Carries ~80% of Vitamin B 12 in blood Vitamin B 12 has half-life of 10-12 days when bound to it
17
Transcobalamin II Molecular weight = 38,000 Alpha globulin NOT a glycoprotein Carries less than 25% of Vitamin B 12 in blood Vitamin B 12 has half-life of under 1 ½ hours when bound to it Encourages absorption in a number of tissues Degenerates once B 12 is released B 12 then recirculates Transcobalamin II deficiency results in pernicious anemia
19
Transcobalamin III R-type binding protein 33% is carbohydrate Molecular weight = 125,000-150,000 Alpha globulin Released from granulocytes Contains more fucose than transcobalamin I
20
Antibacterial Roles of Transcobalamin I & III BBinds to large amounts of vitamin B 12 and carries it to liver EExcreted in bile PPrevents bacteria from using the vitamin for growth
21
Vitamin B 12 separated from Foods in stomach Binds to Transcobalamin I and III Binds to receptors on Liver cells 20% excreted in bile 80% binds to BP & reenters blood Cobalamin Binding Proteins Degraded Within 1 ½ hrs Pinocytosis Returns to liver or Carried to other tissues Released and bound to Transcobalamin II Carried to Ileum and absorbed in by endocytosis BP degenerates, IF binds to cobalamin
23
Sources of Vitamin B 12 Fish Eggs Meat Dairy Products
24
Vitamin B 12 deficiency Cobalamin level in blood = below 200 pg/ mL Common in elderly
25
Causes of Vitamin B 12 Deficiency Malabsorption (inability to absorb food containing cobalamin) Inability to separate cobalamin from food in stomach Lack of recommended intake Inability to use/store cobalamin Proton pump inhibitors Gastritis Stomach/bowel resection Chron’s disease Pancreatitis Gastric lymphoma Myeloma HIV Antibiotics Anticonvulsants Excess Vitamin C Nitric Oxide
26
Symptoms/Effects of Vitamin B 12 Deficiency Pernicious Anemia (Vitamin B 12 is necessary for RBC production) Lethargy Weight loss Weakness Dementia Leucopenia Thrombocytopenia Axonal degeneration Demyelination Urethral Sphincter problems Depression Alzheimer’s Disease Increased liver weight Fat accumulation around heart, liver, peripheral nerves
27
Symptoms/Effects of Vitamin B 12 Deficiency Increase Homocysteine MMA Bilirubin excretion LDH Liver glycogen Mitochondrial cristae in liver Hepatic citrate synthase Propionic acid Succinate dehydrogenase Cytochrome c activity Propionyl CoA Amino Acids Cell metabolism Protein synthesis Fatty acid synthesis enzymes ATP citrate lyase Causes rise in Kreb’s cycle Decrease Transcobalamin II Intrinsic factor
28
Treatment Supplements –Oral pills –Intramuscular –Intranasal –Sublingual
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.