2. 为别的物质甲基化

[[S-腺苷甲硫氨酸（SAM）]]+RH->[[S-腺苷同型半胱氨酸（SAH）]]+-CH_3$

$化学方程式：$

\usepackage{chemfig}
\begin{document}
\chemfig{
	C
		(-[,0.5]H)
		(-[2,0.5]COOH)
		(-[4,0.6]NH_2)
		(-[6,0.5]CH_2
			(-[6,0.5]CH_2
				-[6,0.5]S
					(-[6,0.5]CH_3)
					-[,0.8]
	-[6,0.4]
		(-[0.5,0.65]O-[7.5,0.65])
		<[7,0.5](-[5.5,0.5]O-[4,0.3]H)
		-[,0.5,,, line width=2pt]
		(-[6.5,0.5]OH)>[1,0.5]
	-[2,0.5]N
	-[0.25,0.5]
		(-[7.5,0.5]N=[0.5,0.5]-[2,0.5]N=[3.5,0.5](-[2,0.5]NH_2)-[4.5,0.5]
		(-[3.5,0.5]N=[5,0.6]-[7,0.3])
		=[6,0.5])
				)
			)
}
+\chemfig{
	\fbox{R}H
}

\begin{tikzpicture} 
\draw [->] (0,0) to node[above] {} (1,0); 
\end{tikzpicture}

\chemfig{
	C
		(-[,0.5]H)
		(-[2,0.5]COOH)
		(-[4,0.6]NH_2)
		(-[6,0.5]CH_2
			(-[6,0.5]CH_2
				-[6,0.5]S
					(-[6,0.5]H)
					-[,0.8]
	-[6,0.4]
		(-[0.5,0.65]O-[7.5,0.65])
		<[7,0.5](-[5.5,0.5]O-[4,0.3]H)
		-[,0.5,,, line width=2pt]
		(-[6.5,0.5]OH)>[1,0.5]
	-[2,0.5]N
	-[0.25,0.5]
		(-[7.5,0.5]N=[0.5,0.5]-[2,0.5]N=[3.5,0.5](-[2,0.5]NH_2)-[4.5,0.5]
		(-[3.5,0.5]N=[5,0.6]-[7,0.3])
		=[6,0.5])
				)
			)
}
+\chemfig{
	\fbox{R}-CH_3
}


\end{document}