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The article contains sections titled: 1. History 2. Properties 3. Occurrence 3.1. Abundance 3.2. Ores and Their Origin 3.3. Primary Deposits 3.4. Secondary Deposits 3.5. Recovery of Secondary Platinum Group Metals 3.6. Reserves and Resources 4. Mineral Dressing and Beneficiation 4.1. Treatment of Alluvial Platinum Deposits 4.2. Treatment of Primary Deposits 4.3. Treatment of Nickel Ores 4.4. Treatment of Metal Scrap 4.5. Treatment of Dross 4.6. Treatment of Supported Catalysts 4.7. Treatment of Solutions 5. Dissolution Methods 5.1. Dissolution in Aqua Regia 5.2. Dissolution in Hydrochloric Acid–Chlorine 5.3. Dissolution in Hydrochloric Acid–Bromine 5.4. Other Dissolution Processes 5.5. Dissolution by Salt Fusion 6. Separation of Platinum Group Metals 6.1. Chemistry of Platinum Group Metal Separation 6.2. Older Separation Processes 6.3. Current Separation Processes 6.4. Processes Used in Coarse Separation 6.5. Purification 6.6. Conversion of Salts into Metals 6.7. Partial Purification 6.8. Treatment of Internally Recycled Material 6.9. Construction Materials 7. Platinum Group Metal Compounds 7.1. Inorganic Compounds 7.1.1. Platinum Compounds 7.1.2. Palladium Compounds 7.1.3. Rhodium Compounds 7.1.4. Iridium Compounds 7.1.5. Ruthenium Compounds 7.1.6. Osmium Compounds 7.2. Organic Compounds 8. Alloys 8.1. Alloy Systems 8.2. Special Alloys 8.3. Methods of Treatment 9. Quality Specifications and Analysis 9.1. Quality Specifications 9.2. Qualitative Analysis 9.3. Quantitative Analysis 9.4. Purity Analysis 9.5. Trace Analysis 10. Uses 10.1. Jewelry, Coinage, Investment 10.2. Apparatus 10.3. Heterogeneous Catalysts 10.4. Fuel Cells 10.5. Homogeneous Catalysts 10.6. Automotive Emission Control Catalysts 10.7. Sensors 10.8. Electrical Technology 10.9. Electronics 10.10. Coatings 10.10.1. Coatings Produced by Electrolysis 10.10.2. Coatings Produced by Chemical Reaction 10.10.3. Coatings Produced by Physical Methods 10.11. Dental Materials 11. Economic Aspects 11.1. Supply 11.2. Demand 11.3. Prices 11.4. Commercial Aspects 12. Toxicology

Thermoproteus tenax possesses two different glyceraldehyde-3-phosphate dehydrogenases, one specific for NADP' and the other for NAD' . NADP(H) inhibits the NAD+-specific enzyme competetively with respect to NAD + whereas NAD(H) virtually does not interact with the NADP+-specific enzyme. Both enzymes represent homomeric tetramers with subunit molecular masses of 39 kDa (NADP+-specific enzyme) and 49 kDa (NAD+-specific enzyme), respectively.The NADP+-specific enzyme shows significant homology to the known glyceraldehyde-3-phosphate dehydrogenases from eubacteria and eukaryotes as indicated by partial sequencing.The enzymes are thermostable, the NADP+-specific enzyme with a half-life of 35 min at lOO"C, the NAD+-specific enzyme with a half-line of 220min at lOO"C, depending on the protein concentration. Both enzymes show conformational and functional changes at 60 -70°C.The existence of the extremely thermophilic sulfur-dependent archaebacteria, with growth optima near 100°C and above [l -41, raises questions concerning the thermo-adaptations of their enzyme proteins.Here we describe two ~-glyceraldehyde-3-phosphate dehydrogenases from the sulfur-dependent archaebacterium Thermoproteus tenax (optimal growth temperature 88 "C; upper growth limit 96°C [4]), which differ in their catalytic and molecular properties, and characterize their thermophilic behavior regarding activity and stability. MATERIALS AND METHODS Chemicals and reagentsThe origin of most of the chemicals used and the preparation methods for the enzyme substrates are given in a previous publication [5].Freund's complete adjuvant was obtained from Difco laboratories (Detroit, USA), [U-'4C]sucrose and 3 H 2 0 were from Amersham-Buchler (Braunschweig, FRG), NADPSepharose was from Pharmacia (Uppsala, Sweden).Methods for protein determination, analytical gel chromatography, preparation of polyacrylamide/dodecyl sulfate slab gel electrophoresis, amino acid analysis, tryptic digestion, peptide fractionation, sequencing using 4-dimethylaminoazobenzene-4'-isothiocyanate, and comparisons of peptide sequences and calculation of the activation parameters were described previously [5]. steel fermenters (Bioengineering, Wald, Switzerland) (heterotrophic growth). Cultures were gassed with C 0 2 and, for autotrophic growth, with a mixture of 20% H2 and 80% C 0 2 at 88 "C. The basic medium was as described by Brock et al. [6]. For heterotrophic growth 1% glucose and 0.04% yeast extract were added. Cells were harvested at the late-exponential phase. After cooling the cultures using a heat exchanger and passing through a folded filter (520b 1/2 Schleicher & Schiill, Dassel, FRG) for removing the sulfur, the cells were centrifuged, frozen and stored in liquid nitrogen. Organisms and growth conditions Enzyme assayOxidation of glyceraldehyde 3-phosphate. A previously described procedure [5] was generally followed. The standard assay mixture (pH 7.0 at 70°C) contained 100 mM Tris/HCl, 20 mM 2-mercaptoethanol, 150 mM potassium arsenate, 4 mM ~-glyceraldehyde-3-phosphate and ...

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The primary structure of the glyceraldehyde-3-phosphate dehydrogenase from the archaebacteria shows striking deviation from the known sequences of eubacterial and eukaryotic sequences, despite unequivocal homologies in functionally important regions. Thus, the structural similarity between the eubacterial and eukaryotic enzymes is significantly higher than that between the archaebacterial enzymes and the eubacterial and eukaryotic enzymes. This preferred similarity of eubacterial and eukaryotic glyceraldehyde-3-phosphate dehydrogenase structures does not correspond to the phylogenetic distances among the three urkingdoms as deduced from comparisons of ribosomal ribonucleic acid sequences. Indications will be presented that the closer relationship of the eubacterial and eukaryotic glyceraldehyde-3-phosphate dehydrogenase resulted from a gene transfer from eubacteria to eukaryotes after the segregation of the three urkingdoms.