1. Zinc group elements

2. bulk elements trace elements for some species Periodic Table

3. Other metal ions: less well defined and more obscure roles Zn: Zn: Metalloenzymes Structure promoters Lewis acid Not a redox catalyst! Fe, Cu, Mo: Fe, Cu, Mo: Electron-transfer Redox proteins and enzymes Oxygen carrying proteins Nitrogen fixation

5. Terrestrial distribution: ZnCdHg(relatively low conc.) Distribution in vivo: Zn In human being: ~ 2 g

6. Zn2+ ~ 25-30 % in skin and bones ~ 50 % in the blood ~ 12-20 % plasma ~ 75-80 % erythrocytes ~ 3 % leucocytes Pancreas (-cells) eye

7. Role of Zn2+ : deficiency: disturbances of repr. system dwarfism skin lesions skeletal abnormalities

8. Proteins associated with Zn: 1.H elical: insulin, phospholipase  -sheet: carbonic anhydrase superoxide dismutase 3.M ixed: carboxypeptidase alcohol dehydrogenase 4.R andom: metallothioneins: Zn2+, Cd2+, Hg2+

9. Zn – metalloenzymes: 80! Zn – metalloenzymes: 80! Zn activated enzymes: 20! (Cys – X – Cys) 7 x=nonaromatic amino acid Zn (H 2 O) (1-2) S S S SS(N) N N N O O C

10. Function of Zn in metalloenzymes 1.S tructure-promoter 2.S ubstrate binder 3.L ewis acid

11. reactions catalyzed by Zn- metalloenzymes: hydrolysis of –esters –amides –peptides ad. 1. ad. 2.

12. O O (-) OH Zn 2+ ad 3. Zn 2+ (H 2 O) Zn 2+ (OH - ) + H + R C O R’ + OH - R C O R’ e.g.

13. O = C = O + OH - HCO 3 - Zn 2+ O His C O O (-) H His Zn 2+ O (-) C O H O

14. Cd2+ (toxic): Interferes with:Zn2+, Fe2+ metabolism Cumulates in:kidney liver seminiferous tubules (kills the spermatozoa)

15. Hg –H–H–H–Hg(l)non toxic! –H–H–H–Hg(g)TOXIC –H–H–H–Hg2+(aq)TOXIC Alkyl and aryl mercury toxic Al3+ – L– L– L– Low availability (insoluble ~ pH 7) – O– O– O– Ox. State: +3 (no redox reaction) – A– A– A– Alzheimer’s disease: presenile dementia Alumino-silicate plaques

16. Ga3+, In3+:moderately toxic TI3+, TI+:extremely toxic Pb2+, Pb4+:distinctly toxic Cumulative effect! Intake: ~ 300 mg/day PPPPipe: Pb (HCO3)2 PPPPlants accumulate LLLLead pollution: exhaust emission Pb(C2H5)4 Inhibits the biosynthesis of hem!