Amino acid biosynthesis in isolated pea chloroplasts: metabolism of labeled aspartate and sulfate

Accumulating evidence points to chloroplasts as the site of nitrite and sulfate reduction and incorporation into carbon skeletons [I] Furthermore, several enzymes of aspartate-family amino acid biosynthesis recently have been localized in plastids. These are : aspartate kinase [2] , homoserine dehydrogenase [3] , diaminopimelate decarboxylase [4] , acetolactate synthetase [S] and homocysteine-dependent 5-methyltetrahydrqpteroyl glutamate transmethylase [6]. In whole plants Lys and/or Thr have been shown to regulate the production of the aspartatederived amino acids [7]. Biosynthesis of this family of amino acids and its regulation in isolated chloroplasts has, however, received little attention. In this report we describe the biosynthesis of amino acids in pea chloroplasts from labeled aspartate and sulfate.