ALTERATIONS IN THE ENZYME-ACTIVITY AND PROTEIN CONTENTS OF PROTEIN DISULFIDE-ISOMERASE IN RAT-TISSUES DURING FASTING AND REFEEDING

Protein disulfide isomerase (PDI) is an enzyme that participates in th e formation of disulfide bonds. It is also known to be the subunits of some enzymes and the membrane-associated thyroid hormone-binding prot ein. In this study, we measured the quantitative distribution of PDI p rotein in rat tissues and examined the relationship between protein le vel and enzyme activity in PDI during fasting and refeeding, Western b lotting with specific anti-PDI antiserum detected the PDI protein band of 55 kd, Among several tissues, liver contained the largest amount o f PDI protein, followed by kidney and fat, in which one-third to one-f ourth of the hepatic PDI protein existed. The PDI protein band was als o detected in heart and muscle. Pasting for 3 days decreased PDI prote in levels in rat liver by 40%; control levels were recovered after 3 d ays of refeeding, The same change was observed in kidney. PDI activity , measured by the scrambled ribonuclease method, did not show the para llel alteration to PDI protein level in liver and kidney. Isomerase ac tivity decreased to 50% of control values during fasting, but did not recover by refeeding. Thyroidal status did not affect either PDI prote in level or isomerase activity. These findings show that fasting and r efeeding affect PDI protein and enzyme activity, and that PDI protein level does not always reflect PDI activity. Copyright (C) 1998 by W.B. Saunders Company.