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KMID : 0371619890050010075
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Journal of Wonkwang Medical Science
1989 Volume.5 No. 1 p.75 ~ p.85
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Properties of S-Adenosyl-L-Methionine
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Abstract
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The most activities of S-adenosyl-L-methionine : protein-lysine N-methyltransferase (protein methylase III) were found in the nuclei fraction and only a small activities were distributed in both mitochondrial and microsomal fraction. This enzyme showed a pH optimum around 8.8 in case of using the 02 M Tris-HCI buffer as a protein methylase III assay buffer and was analyzed to be heat-stable. The enzyme reaction was linear with respect to time at least for 30 min. After that time, the velocity was declined gradually and this phenomena was mainly thought to shortage of free enzyme concentration.
The enzyme exhibited classical Michaelis-Menten kinetics when the concentration of S-adenosyl-L-methionine (SAM) was varied. The apparent Km value for SAM was 6.9 X 10-6M. Which is in the same values for other protein methyltransferases.
Cupric ion was evaluated as a potent inhibitor, being inhibited approximately 86 % of activity at 2 mM and the enzyme was inhibited about 40 % by 2 mM ferrousion. When the 2 mM Cue+/5 mM DTT or 2 mM Fe´+/5 mM DTT was added to reaction mixture respectively as a oxidizing system, the additional inhibition was not seen but rather significant increase of activity was revealed in case of Fe"/DTT system. These results were indicated that the highly inhibitory effect of Cu´´ was derived by Cu" in itself not the oxidative effect.
The enzyme was suggested to be histone-specific protein methylase III because only histones among substrates examined, in particular lysine rich histones, were found good substrates.
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