Two Distinct Isozymes of Repair Protein Carboxyl O-Methyltransferase from Porcine Brain

다국어 초록 (Multilingual Abstract)

Protein carboxyl 0-methyltransferase (PCMT) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to free carboxyl groups of methyl-accepting substrate proteins. Two isozymes were separated by DEAE-Sephacel chromatography from porcine brain cytosol and designated PCMT I and II. Isozymes I and II were further purified by adenosy1homocysteine-Sepharose 4B and Superose HR 12 chromatography. The molecular weights of the purified PCMT I and II were determined by mass spectrometry to be 20,138 Da and 25,574 Da, respectively. The two enzymes displayed different isoelectric points; 7.9 for PCMT I and 5.3 for PCMT II. Isozymes I and II exhibited similar substrate specificities when tested with various methyl-accepting proteins. Myelin basic protein, a component of myelinated neurons, was found to be an excellent methyl-accepting substrate for both PCMT isozymes with different K_m values, 21.1 μM for PCMT I and 10.6 μM for PCMT II. The PCMT activity and methyl-accepting capacity displayed similar distribution in the various brain regions with an exception of the lower values in the cerebellum. The overall distribution may relate to a general function of protein repair by PCMT in the brain.

목차 (Table of Contents)

• Introduction
• Materials and Methods
• Results and Discussion