Description:
<jats:title>SYNOPSIS</jats:title><jats:p>A branched‐chain amino acid aminotransferase was extracted from rumen ciliates of the genus <jats:italic>Entodinium</jats:italic> and was partially purified by Sephadex G‐200, DEAE‐cellulose and DEAE‐Sephadex A‐50 column chromatography. The purified enzyme was active only with leucine, isoleucine and valine, and required pyridoxal phosphate as cofactor. The amino acids competed with each other as substrates. The enzyme had optimal activity at pH 6.0 in phosphate buffer. The <jats:italic>K</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub> values for the substrates and cofactor are as follows: 1.66 for leucine; 0.90 for isoleucine; 0.79 for valine; 0.29 mM for α‐ketoglutarate: and 0.1 μM for pyridoxal phosphate. Enzyme activity was inhibited by <jats:italic>p</jats:italic>‐chloromercuribenzoate and HgCl<jats:sub>2</jats:sub>. Gel filtration indicated the enzyme to have a molecular weight of 34,000.</jats:p>