THE STABILITY AND HYDROPHOBICITY OF CYTOSOLIC AND MITOCHONDRIAL MALATE-DEHYDROGENASES AND THEIR RELATION TO CHAPERONIN-ASSISTED FOLDING

mMDH and cMDH are structurally homologous enzymes which show very diff erent responses to chaperonins during folding. The hydrophilic and sta ble cMDH is bound by cpn60 but released by Mg-ATP alone, while the hyd rophobic and unstable mMDH requires both Mg-ATP and cpn10. Citrate equ alises the stability of the native state of the two proteins but has n o effect on the co-chaperonin requirement, implying that hydrophobicit y, and not stability, is the determining factor. The yield and rate of folding of cMDH is unaffected while that of mMDH is markedly increase d by the presence of cpn60, cpn10 and Mg-ATP. In 200 mM orthophosphate , chaperonins do not enhance the rate of folding of mMDH, but in low p hosphate concentrations chaperonin-assisted folding is 3-4-times faste r.