Purification and characterization of alanine racemase from hepatopancreas of black-tiger prawn, Penaeus monodon

Alanine racemase has been purified to homogeneity from the hepatopancreas o f the black tiger prawn. Panaeus mondon. The enzyme depends on pyridoxal 5' -phosphate and consists of two subunits with an identical molecular weight of 41,000. V-max and K-m values for L-alanine are 460 mu mol/min/mg and 50 mM, and those for D-alanine are 94 mu mol/min/mg and 24 mM, respectively. T he enzyme is highly specific toward alanine. Among other amino acids examin ed, only serine served as a substrate: L-serine was racemized at a rate of approximately 0.5% of that of L-alanine. The prawn enzyme is immunochemical ly distinguishable from the enzymes of Bacillus stearothermophilus and Schi zosaccharomyces pombe, which resemble each other. The prawn enzyme is activ ated and stabilized by the presence of monovalent anions including chloride . This is consistent with the previous hypothesis (e.g. E. Fujita, E. Okuma , H. Abe, Comp. Biochem. Physiol. 116A (1997) 83-87) that D-alanine serves as an osmoregulator in marine and euryhaline animals. (C) 2001 Elsevier Sci ence B.V. All rights reserved.