Abstract: D-arginine and L-ornithine are prepared by means of the enzymatic conversion of DL-arginine in the presence of an L-arginase which selectively converts L-arginase to L-ornithine, permitting recovery of both D-arginine and L-ornithine.

Abstract: An arginase batch capable of producing ornithine with reduced consumption of enzyme. The arginase batch is stabilized by the addition of a reducing agent in at least a 10-fold molar amount relative to the arginase.

Abstract: Salts of L-ornithine are prepared by means of the enzymatic conversion of arginine to L-ornithine in the presence of the enzyme L-arginase in an aqueous medium in such a manner that the acid whose salt is to be prepared is used for the adjustment of the pH for the enzymatic conversion and for the subsequent neutralization of the reaction mixture and that the salt formed is isolated directly from the reaction mixture.

Abstract: A substantial elevation of the space-time yield is achieved in the preparation of D-.alpha.-amino acids by means of the biotransformation of hydantoins which are monosubstituted in the 5-position in an aqueous medium in the presence of cells of the microorganism Agrobacterium radiobacter if the biotransformation is carried out under a elevated pressure at the start of the reaction. A further improvement results if this elevated pressure is maintained for a period of at least 16 hours, then removed and the biotransformation continued at atmospheric pressure.