Transcript Biologically Important Inorganic Elements Occurrence and

CHEMISTRY 646
BIOINORGANIC CHEMISTRY
SPRING 2011
Instructor:
Dr. Keith M. Davies.
[email protected]
Office 410 Occoquan (PW1)
703-993-1075
Office Hours: Tu 1:00-3:30; Th 1:30-2:30 (326B ST1)
or by appointment M,W,F at 410 Occoquan (PW1).
.
Syllabus: http://osf1.gmu.edu/%7Ekdavies/646SYL-Spring-11.html
Examinations and Grading
Mid-Term Exam
Tues, March 8th
30%
Final Exam
Tues, May 17th,
40%
1Student
30%
Presentations
1A class
presentation of a “bioinorganic chemistry“ topic
taken from journal articles in the "inorganic-biochemistry"
literature and a 1-2 page written summary.
Textbook:
Biological Inorganic Chemistry, Structure and Reactivity
H. B. Gray, E. I. Stiefel, J. S. Valentine and I. Bertini,
University Science Books, 2007.
Course Material
Jan 25
8
Ligand field effects, magnetic and spectral properties of transition metal
ions. Thermodynamic stability, redox potentials and electron transfer.
Kinetics of metal ion substitution.
Molecular orbital theory for diatomic molecules and coordination
compounds. Bonding models for Π-unsaturated ligands, P-bonded
organometallic systems: Metal carbonyls, P-alkenes, allyls and aromatic
complexes: 16/18-electron rule.
Metal-metal bonds and metal atom clusters. Rationalization of cluster
structures,
Transport and storage of metal ions (Fe, Zn, Cu) in biology. Transferrin,
ferritin, siderophores, metallothioneins, metallochaperones.
Channels and carriers. Mossbauer, epr and IR/Raman vibrational
spectroscopy. Inorganic Tutorial
-----Mid-Term Exam- (Part A) In-Class / Part B (Take Home)-------
15
------------------------------------------Spring Break---------------------------------------
22
Mid-Term Exam Part B (Due)
Dioxygen carriers, cooperativity O2 and CO discrimination. Dioxygen
transport in lower organisms. Inorganic model compounds. Dioxygen
activation enzymes, oxygen atom transfer. Cyt-P450, tyrosinase
Dioxygen toxicity and detoxification enzymes. Superoxide dismutases,
peroxidases and catalases.
Electron transfer proteins: Metal cofactors. Iron cytochromes and iron
sulfur proteins, copper proteins. Electron transfer through proteins.
Feb 1
8
15
22
Mar 1
29
Apr 5
12
19
26
May 3
May 17
Introduction: Occurrence, availability and biological roles of inorganic
elements. Classification of metallobiomolecules. Fundamentals of metal
ion coordination chemistry. Protein structure and metal ion binding.
Metals in Medicine: Cisplatin and analogues. Metal toxicity and metalrelated disease. Chelation therapy.
Nitric Oxide Biochemistry. Physiological roles of nitric oxide. Nitric oxide
synthase enzymes.
Cobalamins: B12-dependant transformations.
Redox cofactors: nitrogenases, hydrogenases.
Hydrolytic chemistry: Metal-dependant (Zn, Ni, Fe) lyase and hydrolase
enzymes. Urease, aconitase
Final Exam 4:30 – 7:15
Text
Chapter
p 695-699
p 675-682
p31-41
p 700-711
p57-77
p139-173
p354-385
p388-395
p319-352
p43-56
p229-253
p261-275
p95-105
p647-653
p562-572
p468-485
p443-450
p175-185
p198-199
p209-212
Bioinorganic Texts in Johnson Center Library
• Bertini, I.; Gray, H. B.; Lippard, S. J.; Valentine, J. S. Bioinorganic
Chemistry (University Science Books; 1994)
• Kaim, W. and Schwederski, B. Bioinorganic chemistry : inorganic
elements in the chemistry of life : an introduction and guide (Wiley,
1994)
• Cowan, J. A. Inorganic Biochemistry: An Introduction (Wiley-VCH: New
York, 1997)
• Lippard, S. J. and Berg, J. M. Principles of Bioinorganic Chemistry
(University Science Books; 1994).
• Roat-Malone, R. M. Bioinorganic Chemistry: A Short Course (Wiley,
2002)
Course Outline and Objectives
 Bioinorganic chemistry is concerned with the roles of
inorganic elements in biological processes.
 In CHEM 646, we will apply fundamental principles of
inorganic chemistry, particularly transition metal
coordination chemistry and ligand field theory, to
understand the structure and function of metal ion
sites in biomolecules.
 We will also consider bioinorganic topics including metal
toxicity, the use of metal complexes as drugs and the
bioregulatory functions of nitric oxide.
The role of the metal center in biomolecules
 Metal ions can have structural roles, catalytic roles, or
both.
 Metals that have catalytic roles will be present at the
active site of the biomolecule which will likely be a
metalloprotein (a metalloenzyme).
 The reactivity of a metalloprotein is defined by the nature
of the metal, particularly its electronic structure and
oxidation state.
 This, in turn, is determined by its coordination
environment (ligand donor atoms) and molecular
geometry, which is provided by the architecture of the
protein surrounding the metal.
The importance of the electronic structure of the
metal center
 The electronic structure and spin state of a metal center
defines its chemical reactivity as a redox center (i.e. it
controls its efficiency at accepting or donating electrons)
 The electronic structure of a metal center defines its
chemical reactivity as a Lewis acid (electron-pair
acceptor) which enables it to bind ligands (O2, N2, CO ..)
for transport, activation and reaction.
 The electronic structure and spin state of a metal center
permits its investigation and characterization through
electronic, Mossbauer and epr spectroscopy and through
magnetic measurements.
Introduction
• Occurrence, availability and biological roles of inorganic elements.
Fundamentals of metal ion coordination chemistry.
• Metal-ligand interactions, stability of metal complexes, chelation.
Review of protein structure and metal ion binding in biomolecules.
Ligand field theory
• Magnetic and spectral properties of transition metal ions.
Thermodynamic stability, redox potentials and Latimer diagrams.
Molecular orbital theory
• Diatomic oxygen species. Metal-ligand s and Π-interactions.
Π-unsaturated ligands, organometallic structures, 18-electron rule
Biological transport and storage of metals
• Iron transport by transferrin and storage in ferritin. Bacterial iron
transport in siderophores. Zn and Cu transport in metallothionein and
metallochaperones..
Dioxygen Transport: O2 carriers
• Hemoglobin, hemerythrin and hemocyanin. Cooperativity in O2
binding, O2 and CO discrimination. Inorganic model compounds.
Oxygen Metabolism: Dioxygen Activation
• Oxygen atom transfer by cytochromes-P450, tyrosinase.
Dioxygen Reactivity and Toxicity
• Toxicity of reduced oxygen species. Oxidative stress from ROS and
detoxification enzymes.
Electron transfer in Biology
• Metal cofactors. Iron cytochromes and iron sulfur proteins. Marcus
theory. Electron transfer in proteins.
Redox Cofactors
• Cobalamins, nitrogenases, hydrogenases.
Metals in Medicine
• Cisplatin and 2nd generation Pt anticancer drugs.
• Metal toxicity and metal-related disease. Chelation therapy.
Nitric Oxide Biochemistry
• Physiological roles of NO in control of blood pressure, neuronal
signaling and cytotoxicity. Nitric oxide synthase enzymes (NOS).
Cobalamins
• B12- coenzme dependant rearrangements.
Hydrolytic Enzymes
• Metal-dependant Zn hydrolase enzymes. Carbonic anhydrase,
carboxypeptidase., alcohol dehydrogenase. Aconitase, urease.
Biological roles and Transport of Na+, K+, Ca2+.
• Na, K, Ca as biological messengers: membrane transport
mechanisms. Ion channels
Occurrence, roles and classification of
metallobiomolecules
Biologically Important Elements
Which “inorganic” elements are important biologically?
99% of human body is comprised of 11 elements
Bulk biological elements: H, C, N, O, P, S, Cl (as PO43-, SO42-, Cl-)
Bulk metal ion nutrients: Na, Mg, K, Ca
Essential elements for a wide range of bacteria/plants/animals
Transition metals: V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo
Non-Metals: (B), F, (Si), Se I, F.
Periodic Distribution of Biologically Important Elements
Evolution of biological roles for
essential metals
Why have certain elements been "selected" for use in
biological systems?
a. their abundance (availability in the earth’s crust or
oceans)
b. their basic fitness (intrinsic chemical suitability)
c. evolutionary adaption to realize critically required
specificity.
• Lighter elements are more abundant in general and therefore utilized
more.
3d metals, rather than 4d, are used as catalytic centers in
metalloenzymes.
• Why has Mo (4d) rather than Cr (3d) been utilized more biologically?
Although Mo is rare in the earth’s crust, Mo is the most abundant
transition metal in sea water as MoO4 has fairly high solubility in water.
Better correlation exists between the abundance of elements in in
human body and in sea water than between the human body and the
earth's crust.
Taken as evidence for the oceans as the site of evolution of life.
• Despite the high abundance of Si, Al and Ti (the 2nd, 3rd and 10th most
abundant elements on earth). Why are they are not utilized biologically?
• Because of the insolubility of their naturally occurring oxides (SiO2,
Al2O3, TiO2) under physiological conditions. A lower oxidation state is
unavailable for Si and Al and unstable for Ti in an aerobic environment
and is readily oxidized to Ti(IV) at pH 7.
•
• Why has iron been used so widely in biology although Fe3+, its most
stable oxidation state, is highly insoluble at pH 7
Complex biological mechanisms have been developed to
accommodate the low solubility of Fe(OH)3 (Ksp = 1 x 1038) ~ pH 7,
and take advantage of its high "availability".
• Co2+ and Zn2+ have very similar coordination chemistry and ionic
size and can be interchanged in many Zn enzymes without loss of
activity. Why is Co not utilized more biologically?
Zn is much more abundant and therefore has been utilized more.
• Why has cobalt been given an essential role in cobalamins despite
its very low availability?
• The unique properties of cobalt (e.g. its oxidation states, redox
potentials and coordination chemistry) is needed to achieve
essential functions of B12 coenzymes.
Indicators of Biologically Important Elements
• Relative abundance of inorganic elements in earth's
crust and in seawater.
• Availability of elements from earth’s crust and sea water
• Elemental composition of human body
• Essential inorganic elements in food
• Inorganic elements linked to deficiency symptoms
Elemental Composition of Human Body (70 kg adult)
Element
mass
mass %
__________________________________________________________________________________________________
Oxygen
O
45.5 kg
65.0
Carbon
C
12.6
18.0
Hydrogen
H
7.0
10.0
Nitrogen
N
2.1
3.0
Calcium
Ca
1.1
1.5
Phosphorus
P
0.700
1.0
Sulfur
S
0.175
0.25
Potassium
K
0.140
0.20
Chlorine
Cl
0.105
0.15
Sodium
Na
0.105
0.15
Magnesium
Mg
35 g
0.020
Iron
Fe
4.2
0.0060
Zinc
Zn
2.3
0.0033
Silicon
Si
1.4
0.0020
Rubidium
Rb
1.1
0.0016
Fluorine
F
0.8
0.0011
Zirconium
Zr
0.3
4.3 x 10-4
Bromine
Br
0.2
2.9 x 10-4
Strontium
Sr
0.14
2.0 x 10-4
Copper
Cu
0.11
1.6 x 10-4
Aluminum
Al
0.10
1.4 x 10-4
Lead
Pb
0.080
1.1 x 10-4
Cadmium
Cd
0.030
Iodine
I
0.030
Manganese
Mn
0.02
Vanadium
V
0.02
Selenium
Se
0.02
Barium
Ba
0.02
Arsenic
As
0.01
Nickel
Ni
0.01
Chromium
Cr
0.005
Cobalt
Co
0.003
Molybdenum
Mo
< 0.00
___________________________________________________________________________________________________
 Mammals are believed to use only 25 of the known elements.
 Eleven non-transition elements that make up 99.9% of the human body
(O, C, H, N, Ca, P, S, K, Cl, Na, Mg),
 Three transition metals, Fe, Zn and Cu are needed in significant amounts.
 “Trace quantities” of many other transition elements are required to
maintain proper physical functioning.
 Other elements in the human body (e.g. Rb, Zr, Sr, Al, Pb, Ba) are not
essential but incorporated inadvertently because they share chemical
and physical properties with essential elements.
 Other elements are added to the list of elements thought to be essential
as our knowledge of the chemistry of living systems increases.
Essential Inorganic Elements in Adult Diet
____________________________________________________________
Recommended Daily Allowance (mg)
____________________________________________________________
K
Na
Ca
Mg
Zn
Fe
Mn
Cu
Mo
Cr
Co
Cl
PO43SO42I
Se
F
2000 - 5500
1100 - 3300
800 - 1200
300 - 400
15
10 - 20
2.0 - 5.0
1.5 - 3.0
0.075 - 0.25
0.05 - 0.2
~ 0.2
3200
800 - 1200
10
0.15
0.05 - 0.07
1.5 - 4.0
_____________________________________________________________
Symptoms of Elemental Deficiency in Humans
__________________________________________________________
Ca
Retarded skeletal growth
Mg
Muscle cramps
Fe
Anemia, immune disorders
Zn
Stunted growth, skin damage, retarded maturation
Cu
Liver disorders, secondary anemia
Mn
Infertility, impaired skeletal growth
Mo
Retarded cellular growth
Co
Pernicious anemia
Ni
Depressed growth, dermatitis
Cr
Diabetes symptoms
Si
Skeletal growth disorders
F
Dental disorders
I
Thyroid disorders
Se
Cardiac muscular weakness
As
Impaired growth (in animals)
________________________________________________________
Biological Roles of Metallic Elements.
Structural
Skeletal roles via biomineralization
Ca2+, Mg2+, P, O, C, Si, S, F as anions, e.g. PO43, CO32.
Charge neutralization.
Mg2+, Ca2+ to offset charge on DNA - phosphate anions
Charge carriers: Na+, K+, Ca2+
Transmembrane concentration gradients ("ion-pumps and channels")
Trigger mechanisms in muscle contraction (Ca). Electrical impulses in nerves (Na, K)
Heart rhythm (K).
Hydrolytic Catalysts: Zn2+ , Mg2+
Lewis acid/Lewis base Catalytic roles. Small labile metals.
Redox Catalysts: Fe(II)/Fe(III)/Fe(IV), Cu(I)/Cu(II), Mn(II)/Mn(III)/(Mn(IV),
Mo(IV)/Mo(V)/Mo(VI), Co(I)/Co(II)/Co(III)
Transition metals with multiple oxidation states facilitate electron transfer - energy transfer.
Biological ligands can stabilize metals in unusual oxidation states and fine tune redox
potentials.
Activators of small molecules.
Transport and storage of O2 (Fe, Cu)
Fixation of nitrogen (Mo, Fe, V)
Reduction of CO2 (Ni, Fe)
Organometallic Transformations.
Cobalamins, B12 coenzymes (Co), Aconitase (Fe-S)
Transition Metals in Biomolecules
Iron.
Most abundant metal in biology, used by all plants and animals including bacteria. Some roles
duplicated by other metals, while others are unique to Fe. Iron use has survived the evolution of
the O2 atmosphere on earth and the instability of Fe(II) with respect to oxidation to Fe(III).
Zinc.
Relatively abundant metal. Major concentration in metallothionein (which also serves as a
reservoir for other metals, e.g. Cd, Cu, Hg). Many well characterized Zn proteins, including redox
proteins, hydrolases and nucleic acid binding proteins.
Copper
Often participatse together with Fe in proteins or has equivalent redox roles in same biological
reactions. Reversible O2 binding, O2 activation, electron transfer, O2- dismutation (SOD).
Cobalt.
Unique biological role in cobalamin (B12-coenzymes) isomerization reactions.
Manganese
Critical role in photosynthetic reaction centers, and SOD enzymes.
Molybdenum
Central role in nitrogenase enzymes catalyzing N2  NH3, NO3  NH3
Chromium, Vanadium and Nickel
Small quantities, uncertain biological roles. Sugar metabolism (Cr);
Ni only in plants and bacteria (role in CH4 production) and SOD enzymes.
Biochemical Classification of
Metallobiomolecules
Transport and storage proteins :
Transferrin (Fe)
Ferritin (Fe)
Metallothionein (Zn)
O2 binding/transport:
Myoglobin (Fe)
Hemoglobin (Fe)
Hemerythrin (Fe)
Hemocyanin (Cu)
Enzymes (catalysts)
Hydrolases:
Carbonic anhydrase (Zn)
Carboxypeptidase (Zn)
Oxido-Reductases:
Alcohol dehydrogenase (Zn)
Superoxide dismutase (Cu, Zn, Mn, Ni)
Catalase, Peroxidase (Fe)
Nitrogenase (Fe, Mo)
Cytochrome oxidase (Fe, Cu)
Hydrogenase (Fe, Ni)
Isomerases:
B12 coenzymes (Co)
Aconitase (Fe-S)
Oxygenases:
Cytochrome P450 (Fe)
Nitric Oxide Synthases (Fe)
Electron carriers:
Electron transferases
Cytochromes (Fe)
Iron-sulfur (Fe)
Blue copper proteins (Cu)
Non Proteins
Transport Agents:
Siderophores (Fe)