A COMPARISON OF THE SECONDARY STRUCTURE OF HUMAN BRAIN MITOCHONDRIAL AND CYTOSOLIC MALIC ENZYME INVESTIGATED BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The secondary structure of human brain cytosolic and mitochondrial 'ma lic' enzymes purified to homogeneity has been investigated by Fourier- transform IR spectroscopy. The absorbance IR spectra of these two isoe nzymes were slightly different, but calculated secondary-structure com positions were essentially similar (38% alpha-helix, 38-39% beta-sheet , 14% beta-turn and 9-10% random structure). These proportions were no t affected by succinate, a positive effector of mitochondrial 'malic' enzyme activity. IR spectra indicate that the tertiary structures of h uman brain cytosolic and mitochondrial 'malic' enzymes are slightly di fferent, and addition of succinate does not cause conformational chang es to the tertiary structure of the mitochondrial enzyme. Thermal-dena turation patterns of the cytosolic and mitochondrial enzymes, obtained from spectra recorded at different temperatures in the absence or pre sence of Mg2+, suggest that the tertiary structure of both isoenzymes is stabilized by bivalent cations and that the cytosolic enzyme posses ses a more compact tertiary structure.