A thermodynamic screening of 31 pure component working fluids for organic Rankine cycles (ORC) is given using BACKONE equation of state. The fluids are alkanes, fluorinated alkanes, ethers and fluorinated ethers. The ORC cycles operate between 100 and 30 1C typical for geothermal power plants at pressures mostly limited to 20 bar, but in some cases supercritical pressures are also considered. Thermal efficiencies Z th are presented for cycles of different types. In case of subcritical pressure processes one has to distinguish (1) whether the shape of the saturated vapour line in the T,s-diagram is bell-shaped or overhanging, and (2) whether the vapour entering the turbine is saturated or superheated. Moreover, in case that the vapour leaving the turbine is superheated, an internal heat exchanger (IHE) may be used. The highest Z th -values are obtained for the high boiling substances with overhanging saturated vapour line in subcritical processes with an IHE, e.g., for n-butane Z th ¼ 0.130. On the other hand, a pinch analysis for the heat transfer from the heat carrier with maximum temperature of 120 1C to the working fluid shows that the largest amount of heat can be transferred to a supercritical fluid and the least to a high-boiling subcritical fluid. r

The orphan receptor ChemR23 is a G-protein coupled receptor (GPCR) with homology to neuropeptide and chemoattractant receptors. Tazarotene, a synthetic retinoid activating retinoic acid receptor (RAR), up-regulates tazaroteneinduced gene-2 (TIG2). The function and molecular target of this protein are now described. By means of reverse pharmacology screening using a peptide library generated from human hemo¢ltrate, we have isolated and identi¢ed TIG2 as the natural ligand of ChemR23 and report the speci¢c molecular form of the bioactive, circulating TIG2, representing the amino-acid residues 21 to 154 of the 163 amino acid-containing prepropeptide. Based on the expression pattern of ChemR23 and TIG2, the physiological role in bone development, immune and in£am-matory responses and the maintenance of skin is now being investigated.

Using streptolysin-O (SLO) we have developed a permeabilized cell system retaining the competence to import proteins into peroxisomes. We used luciferase and albumin conjugated with a peptide ending in the peroxisomal targeting sequence, SKL, to monitor the import of proteins into peroxisomes. After incubation with SLO-permeabilized cells, these exogenous proteins accumulated within catalase-containing vesicles. The import was strictly signal dependent and could be blocked by a 10-fold excess of peptide containing the SKL-targeting signal, while a control peptide did not affect the import. Peroxisomal accumulation of proteins was time and temperature dependent and required ATP hydrolysis. Dissipation of the membrane potential did not alter the import efficiency. GTP-hydrolyzing proteins were not required for peroxisomal protein targeting. Depletion of endogenous cytosol from permeabilized cells abolished the competence to import proteins into peroxisomes but import was reconstituted by the addition of external cytosol. We present evidence that cytosol contains factors with SKL-specific binding sites. The activity of cytosol is insensitive to N- ethylmaleimide (NEM) treatment, while the cells contain NEM-sensitive membrane-bound or associated proteins which are involved in the import machinery. The cytosol dependence and NEM-sensitivity of peroxisomal protein import should facilitate the purification of proteins involved in the import of proteins into peroxisomes.

Lysosomal acid phosphatase (LAP) is synthesized as a transmembrane protein with a short carboxy‐terminal cytoplasmic tail of 19 amino acids, and processed to a soluble protein after transport to lysosomes. Deletion of the membrane spanning domain and the cytoplasmic tail converts LAP to a secretory protein, while deletion of the cytoplasmic tail as well as substitution of tyrosine 413 within the cytoplasmic tail against phenylalanine causes accumulation at the cell surface. A chimeric polypeptide, in which the cytoplasmic tail of LAP was fused to the ectoplasmic and transmembrane domain of hemagglutinin is rapidly internalized and tyrosine 413 of the LAP tail is essential for internalization of the fusion protein. A chimeric polypeptide, in which the membrane spanning domain and cytoplasmic tail of LAP are fused to the ectoplasmic domain of the Mr 46 kd mannose 6‐phosphate receptor, is rapidly transported to lysosomes, whereas wild type receptor is not transported to lysosomes. We conclude that a tyrosine containing endocytosis signal in the cytoplasmic tail of LAP is necessary and sufficient for targeting to lysosomes.

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