Characterization of IMT1, myo-inositol O-methyltransferase, from Mesembryanthemum crystallinum

Arch Biochem Biophys. 1995 Sep 10;322(1):183-8. doi: 10.1006/abbi.1995.1450.

Abstract

A full-length transcript, Imt1, encoding myo-inositol O-methyltransferase (EC 2.1.1.X) from the halophyte Mesembryanthemum crystallinum was expressed in Escherichia coli. The enzyme, IMT1, uses S-adenosyl-L-methionine to methylate myo-inositol to form D-ononitol. IMT1 with a monomeric mass of 41,000 was isolated by ammonium sulfate fractionation, gel filtration and ion exchange chromatography to apparent purity on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminal amino acid sequence of the purified recombinant enzyme was identical to that encoded by the cDNA sequence. The apparent Km for S-adenosylmethionine was 0.18 mM with a Vmax of 1550 pkat/mg protein. The Km for myo-inositol was 1.32 mM. The reaction became substrate-inhibited by concentrations of S-adenosylmethionine greater than 0.5 mM. Inositol methyltransferase was competitively inhibited 50% with 0.01 mM S-adenosyl-homocysteine, while 1 mM homocysteine, homoserine, or adenosine did not inhibit. The enzyme exhibited a pH optimum of 7.8 and a temperature optimum of 37 degrees C. Activity of the isolated inositol methyltransferase was stable when stored at 4 degrees C.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • DNA, Plant / genetics
  • Escherichia coli / genetics
  • Inositol / analogs & derivatives
  • Inositol / chemistry
  • Kinetics
  • Methyltransferases / genetics
  • Methyltransferases / isolation & purification
  • Methyltransferases / metabolism*
  • Molecular Sequence Data
  • Molecular Weight
  • Plants / enzymology*
  • Plants / genetics
  • Recombinant Proteins / genetics
  • Recombinant Proteins / isolation & purification
  • Recombinant Proteins / metabolism
  • S-Adenosylhomocysteine / metabolism
  • S-Adenosylmethionine / metabolism
  • Stereoisomerism
  • Substrate Specificity

Substances

  • DNA, Plant
  • Recombinant Proteins
  • Inositol
  • S-Adenosylmethionine
  • S-Adenosylhomocysteine
  • Methyltransferases
  • inositol O-methyltransferase