TRACE METALS - FROM DEFICIENCY TO TOXICITY

1. TRACE METALS - FROM DEFICIENCY TO TOXICITY Quest – July 22, 2004 Yeala Shaked, Yan Xu and Francois Morel, Geosciences Dept, Ecology and Evolutionary Biology Dept. and Princeton Environmental Institute

2. Trace Metals (red label - metals with known biological role) The transition metal elements V, Mo, W, Mn, Fe, Co, Ni, Cu, and Zn serve as osmotic regulators, as structural glue, and as catalytic centers for hundreds of cellular reactions. About one third of all characterized enzymes are metalloenzymes.

3. TRACE METALS - FROM DEFICIENCY TO TOXICITY Average elemental composition of a human body (for a 70 kg adult in units of grams) O- 45500, C- 12600, H- 7000, N- 2100, Ca- 1050 , P- 700 , S- 175, K- 140 , Cl- 105 , Na- 105, Mg- 35 Fe- 4.2 , Zn- 2.3, Si- 1.4 ,F-0.8 ,Cu- 0.11 , I -0.03,Mn -0.02 ,Se-0.02, V- 0.02

4. Nutritional supplements Adaptive strategies- metal replacements, alternative pathways Chelation therapy Cellular response-Metal efflux, metal chelation Growth rate of unicellular algae Enzyme activity Tissue function Toxicity Deficiency

5. Metal Toxicity: • Non specific binding to biomolecules- destruction of structure and function • 2. Replacement of original metal by the toxicant metal, which lack the ability to carry the original function.

6. Today’s Lecture + lab: • Demonstrating the concept of trace metal deficiency and toxicity • using the Zn metalloenzyme Alkaline Phosphatase • Alkaline Phosphatase – • - Abundance and significance- role of P in the human body and the environment • Reaction mechanism • Active center – 2 Zn atoms • Metal removal by EDTA • - Lab instructions

7. 2 MG ions4 ZN ions 2 PO4 Alkaline phosphatase (AP) An enzyme that catalyzes the cleavage of a phosphate group from a variety of compounds. It is found in most tissues and organs in our body and in most organisms and is important in recycling phosphate within living cells. It seems to be particularly prevalent in tissues that are transporting nutrients, including intestine and kidney. AP is essential for the deposition of minerals in the bones and teeth among many other functions. Blood levels tests of AP serve as indicative tool forbones growth, liver cells damage and other diseases. E.Coli Alkaline Phosphatase

8. Role of P in human nutrition • * Humans obtain P from eating plants, and use it to make bones, teeth, and shells. It is also an important constituent of cell membranes, DNA, RNA, and ATP. • * On average, the human body contains 1 3/4 lb of P, with the overwhelming amount found in bones. The remainder is used for other body processes including the metabolism of red blood cells and ATP production. ATP is an energy-rich compound that fuels activity in the body's cells. * Phosphorus is excreted as phosphate and organic-P compounds. Soil microbes recycle P for plant uptake, thereby making it available to all animals.

9. P in the Environment In aquatics environments (mostly lakes) phosphate concentration is often limiting phytoplankton growth. Organic P compounds are potentially large source of P. However, since microorganisms can not access those compounds, the enzymatic degradation and release of available PO43- by Alkaline phosphatase is of large environmental significance.

10. Alkaline Phosphatase- Active site contains two Zn atoms and Mg Active site of E. coli Alkaline Phosphatase The Zn atoms play a catalytic role in the reaction e.g. activating the oxygen of the water or alcohol, and stabilizing the leaving group The Mg atom has a structural role

11. Alkaline Phosphatase activity assay: phosphate cleavage from p-Nitrophenyl phosphate p-Nitrophenyl phosphate AP + H2O phosphate p-Nitrophenol + absorbance at 410nm

12. The EDTA Molecule * EDTA or ethylenediaminetetraacetic acid is a novel molecule for complexing metal ions. * It is a polyprotic acid containing four carboxylic acid groups (acidic hydrogens are red) and two amine groups with lone pair electrons (green dots).  * On a worldwide basis over 100,000 metric tons are produced annually. Because of its strong complexing ability for most metal ions, it is used in the food industry as a sequestering agent.  The complexing of the metal ion may prevent further reactions, such as binding metals that are cofactors for enzymes, or just remove a metallic taste, such as metal contamination added during processing.  

13. Lab plan: Goal- Demonstrating the concept of metal deficiency and toxicity using E. coli Alkaline phosphatase. Enzyme activity assay (color forming reaction) with different levels of Zn. pH buffer enzyme substrate Metal chelator Metals 36 ul

14. Lab instructions: