Biochemistry of Minerals P Na K Ca Mg Cl Biological forms of minerals in living systems Fe Zn Cu Mn Se Co V Si As Mo I Br F

Characteristics of Biochemical Ion Complexes Na+, K+ Mg2+,Ca2+ Zn2+, Ni2+ Fe, Cu, Co, Mo, Mn Favored Oxidation state +1 +2 Variable, more than one state Stability of complex Very low Low to medium High High (medium for Mn2+ and Fe2+) Favored donor atoms Oxygen Sulfur or nitrogen Sulfur or nitrogen (oxygen for Mn and Fe) Mobility in biological media Very mobile Semi mobile Static Static, semi mobile for Mn2+ and Fe2+ After Frausto de Silva and Williams

Glucose Na+ Mg2+ Mn2+ K+ Ca2+ PO43- Hemoglobin O2 Fe2+ H2O Cu2+ intestine Na+ liver Mg2+ Mn2+ K+ Ca2+ PO43- mitochondria Hemoglobin O2 Fe2+ H2O Cu2+

Inorganic Enzyme Cofactors (one-third of all enzymes require a metal ion for catalytic function)

Metalloenzymes vs Metal Activated Enzymes 1. Metal in equilibrium Metal firmly affixed to protein 2. Activated by adding metal ion Adding metal has minimal effect 3. Metal lost on isolation Metal stays bound, removable by chelators 4. No stoichiometry with protein Integral number per protein 5. Electrostatic bonding Coordinate covalent bonding 6. Multiple metal binding sites Limited number, generally one 7. Binding sites, angles irregular Binding sites exhibit specific geometry Mostly group IA and IIA metals Na+, K+, Mg2+. Ca2+ Mostly 3d transition metals Zn2+, Fe2+. Cu2+, Co2+

Examples of Metalloenzymes Zinc (over 300) Manganese Arginase Water splitting enzyme Pyruvate carboxylase Dehydrogenases RNA, DNA polymerase Carbonic anhydrase Carboxypeptidase Amino peptidase Cobalt (with B12) Methylmalonyl CoA mutase Homocysteine transmethylase Copper Superoxide dismutase Tyrosinase Cytochrome oxidase (with Fe) Lysyl oxidase Peptide amidating Dopamine beta hydroxylase Molybdenum Nitrogenase Xanthine oxidase Calcium Iron Thermolysin Ribonucleotide reductase Cytochrome oxidase (with Cu) Nickel Urease

Quick Overview of Mineral Functions Zn2+ Na+, K+, Cl- Osmotic control Electrolyte equilibria Ion currents Gated channels Lewis acid Enzyme cofactor Protein structure Hormone activator Neurotransmitter Genetic expression regulator Mg2+ Fe2+, Fe3+ Phosphate metabolism Heme iron Electron transport Oxygen activator Oxygen carrier Ca2+ Muscle contraction Cell signaling Enzyme cofactor Blood clotting Mineralization Morphogenesis Gene regualtion Cu+, Cu2+ Enzyme cofactor Oxygen carrier Oxygen activator Iron metabolism

Quick Overview (cont.) Se Cr3+ Redox reactions Antioxidant Insulin mimetic Glucose metabolism Mo2+ Mn2+ Enzyme cofactor Nitrogen activator Enzyme cofactor (limited) HPO4=, Si Ni2+ Coenzyme Remnant of early life Acid-base non metals Biomineralization Co3+ Vitamin b12

Examples of Metalloproteins Function 1. Metallothionein Cu, Zn, Cd storage, heavy metal buffer 2. Ferritin Iron storage, iron buffer 3. Calmodulin Ca binding, allosteric regulator 4. Transferrin Iron transport 5. Selenoprotein W Selenium transport 6. Calbindin Calcium transport

Biomineralization Calcium and phosphate Bones and Teeth

Cross section through trebecular and cortical bone revealing the internal architecture surrounded by marrow tissue. Cortical bone with Halversion system (a series of channels supplying nutrients). Black dots are osteocytes Leg bone of a horse showing the trebecular (spongy) bone and the cortical (solid) bone. This bone is able to withstand forces generated by this 1,500 lb animal Trebecular bone of the lower spine. Changes with aging.

Demineralized bone: Shown is he organic matrix consisting mostly of collagen upon which the bone crystals are laid.

Hydroxyapatite (crystal structure) Ca10(PO4)6 OH2 Ca P O H

Zinc Function 300 enzymes require zinc numerous hormones require zinc DNA, RNA polymerases numerous hormones require zinc insulin EGF transcription factors (zinc finger proteins) membrane stability myelination skeletal development

Metal Ions in Catalysis- One third of all enzymes require a metal ion for catalysis

Zn 2+Polarizes H2O, making it a better nucleophile His –Zn2+ His O H .. + C His –Zn2+ His O H C H2O His –Zn2+ His O H .. + H+ + H C Bicarbonate Displaces HCO3-

Biochemical Iron Hemoglobin- oxygen carrier in the blood Myoglobin- O2 carrier in cells (mostly in muscle) Cytochromes- electron carriers in membranes Catalase- enzyme that destroys H2O2 (hydrogen peroxide) Cytochrome oxidase- electron transport, ATP synthesis in mitochondria Cytochrome P450- detoxifying enzyme Nitrogenase- nitrogen fixation Ferritin- iron storage in cells, plasma Transferrin- iron transport in blood Iron-sulfur electron proteins- electron carriers Tyrosine and phenylalanine hydroxylase- enzymes that synthesizes L-DOPA and tyrosine, respectively Ribonucleotide reductase- enzyme that forms deoxyribose from ribose

Function Oxygen Transport & Storage Hemoglobin Myoglobin Electron Transport & Energy Metabolism Cytochromes Fe-S proteins Substrate Oxidation & Reduction – Iron dependent enzyme- Ribonucleotide reductase Amino acid oxidases Fatty acid desaturases Nitric oxide synthetase Peroxidases HEME is synthesized in the liver from succinyl-CoA and Glycine. Hemoglobin represents more than 95% of the proteins of the red blood cell, and contains about 60% of the body iron. Function1) transport O2from the respiratory organ to peripheral tissue 2)Transport of CO2 and proteins from peripheral tissues t the lung for subsequent excretion 3)transport NO. 2,3-bisphosphoglycerate, an intermediate in glycolysis, stabilizes the tettrameric structure of hemoglobin, indicateing another important function of glycolysis in the functions of red blood cells. (Iron dificient, heme decreases leading O2 transport and NO transport decrease--- Vascular systeem decreases and immune system decrease) Myoglobin is a single polypeptide chain (MW16900). Contains about4% of the body’s iron. Myoglobin is the minor protein of muscle cells and is used for the short term storage of oxygen. Electron transport: In cytochromes, the oxidation and reduction of the iron atom are essential to their biological function. By contrast, oxidation of the Fe2+ to Fe3+ of hemoglobin or myoglobin destroys biological activity. All use O2 as a substrate

Examples of Iron-dependent Enzymes Aldehyde Oxidase R-CHO + O2  RCOOH + H-O-O-H Tryptophan 5-monooxygenase L-tyrptophan + BH4 + O2  5 OH L-tryptophan + BH2 + H2O Fatty Acid desaturase Stearoyl-CoA + NADH + H+ + O2  Oleoyl-CoA + NAD+ + 2H2O Peroxidase 2H2O2  2H2O + O2 (O2 is either incorporated into the product or reduced by electrons)

Electron Transport Complexes Membranes bound heme proteins or “cytochromes” Iron-Sulfur proteins..high reducing potential Mobile electron carriers Coenzyme Q Cytochrome c

.. .. .. .. .. .. .. .. Reduced Oxidized Transport Mechanism A bucket-brigade .. .. Cyt a+a3 (Fe3+) (Fe2+) .. .. Cyt b (Fe3+) (Fe2+) Cyt c1 (Fe3+) (Fe2+) Cyt c (Fe3+) (Fe2+) NADH FMN FMNH2 CoQ CoQH2 O2 H2O NAD+ .. .. .. .. Reduced Oxidized + 0.82 volts -0.32 volts

Iron and Molybdenum in Nitrogenase - H N = 2 F d e R A T P D . 9 4 3 c t i v a Electron Transfer “Pump” Dinitrogenase Dinitrogenase Reductase e + H+ Fe N2 + 3H2  2NH3