Analysis of the enzymatic properties of a broad family of alanine aminotransferases

PLoS One. 2013;8(2):e55032. doi: 10.1371/journal.pone.0055032. Epub 2013 Feb 7.

Abstract

Alanine aminotransferase (AlaAT) has been studied in a variety of organisms due to the involvement of this enzyme in mammalian processes such as non-alcoholic hepatocellular damage, and in plant processes such as C4 photosynthesis, post-hypoxic stress response and nitrogen use efficiency. To date, very few studies have made direct comparisons of AlaAT enzymes and fewer still have made direct comparisons of this enzyme across a broad spectrum of organisms. In this study we present a direct kinetic comparison of glutamate:pyruvate aminotransferase (GPAT) activity for seven AlaATs and two glutamate:glyoxylate aminotransferases (GGAT), measuring the K(M) values for the enzymes analyzed. We also demonstrate that recombinant expression of AlaAT enzymes in Eschericia coli results in differences in bacterial growth inhibition, supporting previous reports of AlaAT possessing bactericidal properties, attributed to lipopolysaccharide endotoxin recognition and binding. A probable lipopolysaccharide binding region within the AlaAT enzymes, homologous to a region of a lipopolysaccharide binding protein (LBP) in humans, was also identified in this study. The AlaAT enzyme differences identified here indicate that AlaAT homologues have differentiated significantly and the roles these homologues play in vivo may also have diverged significantly. Specifically, the differing kinetics of AlaAT enzymes and how this may alter the nitrogen use efficiency in plants is discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine Transaminase / chemistry
  • Alanine Transaminase / metabolism*
  • Amino Acid Sequence
  • Animals
  • Gram-Negative Bacteria / enzymology
  • Gram-Negative Bacteria / growth & development
  • Humans
  • Molecular Sequence Data
  • Phylogeny
  • Sequence Homology, Amino Acid
  • Substrate Specificity

Substances

  • Alanine Transaminase

Grants and funding

This research was funded by an NSERC Discovery Grant - NSERC RGPIN 89739 to the Principal Investigator, AGG (http://www.nserc-crsng.gc.ca/), and a Research grant from the Alberta Crop Industry Development Fund; ACIDF2009C001R to AGG (URL http://www.acidf.ca/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.