ABSTRACT
The COT1 gene of Saccharomyces cerevisiae has been isolated as a dosage-dependent suppressor of cobalt toxicity. Overexpression of the COT1 gene confers increased tolerance to cobalt and rhodium ions but not other divalent cations. Strains containing null alleles of COT1 are viable yet more sensitive to cobalt than are wild-type strains. Transcription of COT1 responds minimally to the extracellular cobalt concentration. Addition of cobalt ions to growth media results in a twofold increase in COT1 mRNA abundance. The gene encodes a 48-kDa protein which is found in mitochondrial membrane fractions of cells. The protein contains six possible membrane-spanning domains and several potential metal-binding amino acid residues. The COT1 protein shares 60% identity with the ZRC1 gene product, which confers resistance to zinc and cadmium ions. Cobalt transport studies indicate that the COT1 product is involved in the uptake of cobalt ions yet is not solely responsible for it. The increased tolerance of strains containing multiple copies of the COT1 gene is probably due to increased compartmentalization or sequestration of the ion within mitochondria.
Subject(s)
Cobalt/metabolism , Fungal Proteins/genetics , Genes, Fungal , Saccharomyces cerevisiae Proteins , Saccharomyces cerevisiae/genetics , Amino Acid Sequence , Base Sequence , Biological Transport , Cation Transport Proteins , Cloning, Molecular , DNA, Fungal , Drug Resistance, Microbial/genetics , Fungal Proteins/analysis , Immunoblotting , Intracellular Membranes/chemistry , Membrane Transport Proteins , Mitochondria/chemistry , Molecular Sequence Data , Phenotype , Restriction Mapping , Saccharomyces cerevisiae/growth & development , Saccharomyces cerevisiae/metabolism , Sequence Homology, Nucleic AcidABSTRACT
The development of topical drug products requires testing for skin toxicology reactions. A variety of patch test systems are available with which chemicals are applied to skin. The purpose of this study was to determine the skin absorption of paraphenylenediamine (PPDA) from a variety of such systems. [14C]-PPDA (1% pet., USP) was placed in a variety of patch test systems at a concentration normalized to equal surface area (2 mg/mm2). Skin absorption was determined in the guinea pig by urinary excretion of 14C. There was a six-fold difference in the range of skin absorption (p less than 0.02). In decreasing order, % skin absorption from the systems were Hill Top Chamber (53.4 +/- 20.6) greater than Teflon Control patch (48.6 +/- 9.3) greater than Small Finn Chamber with paper disc insert (34.1 +/- 19.8) greater than Small Finn Chamber (29.8 +/- 9.0) greater than Large Finn Chamber (23.1 +/- 7.3) greater than AL-Test Chamber (8.0 +/- 0.8). Thus, the choice of patch system could produce a false negative error if the system inhibits skin absorption, with a subsequent skin toxicology reaction.
