[33] S-adenosylmethionine: ε-N-l-lysine methyltransferase

This chapter discusses the assay procedure, purification, and properties of the S-adenosylmethionine: ɛ-N-lysine methyltransferase. The initial extract for the assay is prepared from Neurospora crassa 33933. The methyllysine transferase assay measures the formation of radioactive methylated lysine derivatives following incubation of appropriate lysine substrates with [methyl-3H]AdoMet. The purification procedure is also tabulated in the chapter. The purification scheme yields a highly purified protein that is homogeneous following column chromatography, polyacrylamide gel electrophoresis, and ultracentrifugation in which lysine methyltransferase activity for Reactions A, B, and C remains relatively constant. S-Adenosylmethionine: ɛ- N-L-lysine methyltransferase as prepared herein from N. crassa is devoid of protein methylase III activity; but N. crassa contains a cytochrome c-specific proteinlysine methyltransferase. The molecular weight of the lysine methyltransferase is estimated to be 22,000 based on sedimentation equilibrium and molecular filtration data and 24,000 based on amino acid analysis assuming two methionine residues per mole protein. The protein appears to be devoid of subunit structure based on observations from sedimentation equilibrium analysis of the protein in 6 M guanindine hydrochloride and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both carnitine and trimethyllysine repress synthesis of lysine methyltransferase in growing cultures of N. crassa.