0. 利用现成嘌呤核苷或嘌呤碱重新合成嘌呤核苷酸：磷酸核糖转移酶

[[0. 核苷酸（Nucleotide）]]+$<->[[碱基]]+[[5-磷酸核糖焦磷酸（PRPP）]]

\usepackage{chemfig}
\begin{document}

\chemfig{
	(-[3,0.25])
	(<:[,0.7]base)
	-[5.5,0.5]
		(<:[7,0.7]OH)
	-[3.8,0.5]
		(<:[5,0.7]HO)
	-[2.2,0.5]
		(-[0.5,0.5]O)
		(<[3.5,0.7]-[4.5,0.8]\fbox{P}n)
}
+$

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

\chemfig{
	(-[3,0.25])
	(<:[0.3,0.8]\fbox{P}-[7.8,0.8]\fbox{P})
	-[5.5,0.5]
		(<:[7,0.7]OH)
	-[3.8,0.5]
		(<:[5,0.7]HO)
	-[2.2,0.5]
		(-[0.5,0.5]O)
		(<[3.5,0.7]-[4.5,0.8]\fbox{P})
}

+base

\end{document}

具体

• [[腺嘌呤磷酸核糖转移酶（APRT）]]补救[[0. A：腺嘌呤（adenine）]]

• [[次黄嘌呤-鸟嘌呤磷酸核糖转移酶（HGPRT）]]补救[[G：鸟嘌呤（guanine）]]和[[次黄嘌呤（hypoxanthine）]]