Purification and Some Properties of Bovine Liver Cytosol Thioltransferase

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Abstract
A cytosol thioltransferase was purified 37,000-fold from bovine liver by essentially the same procedure as reported for rat liver enzyme by Axelsson et al. ((1978) Biochemistry17, 2978–2984). The purified enzyme appears to be homogeneous on sodium dodecyl sulfate (SDS)-gel electrophoresis and has a molecular weight (Mr) of 11,000, an isoelectric point (pI) of 8.1, and an optimum pH with S-sulfocysteine and GSH as substrates of 8.5. It is specific for disulfides including l-cystine, S sulfocysteine, ribonuclease A, trypsin, soybean Kunitz trypsin inhibitor, soybean Bowman Birk trypsin inhibitor and insulin, and converts Bowman Birk trypsin inhibitor to an inactive form. The enzyme does not act as a protein : disulfide isomerase, as measured by reactivation of “scramble” ribonuclease and Kunitz soybean trypsin inhibitor. Thioltransferase activity was found in cytosol of various bovine tissues.