An endogenous proteinacious inhibitor in porcine liver for S-adenosyl- l-methionine dependent methylation reactions: identification as oligosaccharide-linked acyl carrier protein

• Published in: The international journal of biochemistry & cell biology 2000-04, Vol.32 (4), p.455-464
• Main Authors: Hong, Sung Youl, Lee, Hoi Young, Kim, Sangduk, Paik, Woon Ki, Lee, Hyang Woo, Seo, Dong Wan, Moon, Hyung In, Han, Jeung Whan
• Format: Article
• Language: English
• Subjects: Acyl Carrier Protein - chemistry; Acyl Carrier Protein - isolation & purification; Animals; Endogenous inhibitor; Enzyme Inhibitors - chemistry; Enzyme Inhibitors - isolation & purification; Kinetics; Liver - chemistry; Magnetic Resonance Spectroscopy; Methylation; Methyltransferases - antagonists & inhibitors; Methyltransferases - chemistry; Molecular Weight; Oligosaccharide-linked acyl carrier protein; Oligosaccharides - chemistry; Peptide Fragments - chemistry; Protein Methyltransferases - chemistry; Rats; S-Adenosylmethionine - chemistry; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Swine; Transferases (Other Substituted Phosphate Groups) - chemistry; Transmethylation
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/S1357-2725(99)00144-2

A proteinacious inhibitor of S-adenosyl- l-methionine (AdoMet)-dependent transmethylation reactions was purified to homogeneity from porcine liver by size exclusion chromatography and FPLC. The molecular weight of the inhibitor was 12,222 Da. A 7400 Da polypeptide fragment of the purified inhibitor was sequenced by matrix-associated laser desorption ionization; time-of-flight MS, and was found to be identical with the known sequence of spinach acyl carrier protein (ACP). Although the remainder of the molecule was not clearly defined, 1H and HH correlation of spectroscopy (COSY) NMR analysis revealed the presence of an oligosaccharide with α-glycosidic linkage. The purified oligosaccharide-linked ACP inhibited several AdoMet-dependent transmethylation reactions such as protein methylase I and II, S-farnesylcysteine O-methyltransferase, DNA methyltransferase and phospholipid methyltransferase. Protein methylase II was inhibited with a K i value of 2.4×10 −3 M in a mixed inhibition pattern, whereas a well-known competitive product inhibitor S-adenosyl- l-homocysteine (AdoHcy) had K i value of 6.3×10 −6 M. Commercially available active ACP fragments (65–74) and ACP from Escherichia coli had less inhibitory activity toward S-farnesylcysteine O-methyltransferase than the purified inhibitor. The biological significance of this oligosaccharide-linked ACP which has two seemingly unrelated functions (inhibitor for transmethylation and fatty acid biosynthesis) remains to be elucidated.