On the compartmentalization of catalase,fatty acyl-CoA oxidase and urate oxidase in mammalian livers,and the influence of clofibrate treatment on this microlocalization

The compartmentalization of catalase, fatty acyl-CoA oxidase and urate oxidase was examined in the livers of mice, rats and guinea pigs, using the technique of digitonin extraction in order to avoid the trauma associated with centrifugation procedures. The results are interpreted as indicating that an appreciable proportion of catalase activity occurs in the cytoplasmic compartment of these cells. Following treatment of the animals with clofibrate, the specific activity in both peroxisomal and cytoplasmic compartments was increased, with a higher proportion of cytoplasmic catalase being evident in mice. The results for catalase were compared with those for fatty acyl-CoA oxidase and urate oxidase both of which were indicated as showing a closer association with the peroxisomal compartment than was the case for catalase. These data have been discussed in relation to their significance on present understanding of peroxisomal structure and function.     

The tail of a chaperonin: the C-terminal region of Esctierichia coli GroEL protein

The active form of the KSP60 molecular chaperone of Escherichia coli, GroEL, is a pair of seven-membered rings. We have used site-directed mutagenesis to construct forms of the 547-amino-acid monomer truncated at the C-terminus. We show here that forms that are 520 amino acids long or longer are close to being fully functional. Removing one further amino acid, however, results in a protein, GroEL519, which retains little function. This truncated form is metabolically stable but is not recovered from the cell in particle form. When synthesized at high levels, it prevents the normal assembly of GroEL547 present in the same cell. When synthesized at low levels, it can be included, probably at low molar ratios, in particles formed by assembly-competent forms of GroEL. This can be seen as partial complementation of the temperature-sensitive mutant groEL44. We conclude that amino acid 520 is cruical for particle assembly. GroEL516 has in vivo properties similar to those of GroEL519, but the still shorter form, GroEL504, appears to be inactive.