McCarthy S A, Mattheis J R, Rebeiz C A
Biochemistry. 1982 Jan 19;21(2):242-7. doi: 10.1021/bi00531a007.
The operation of two parallel biosynthetic pathways during the biosynthesis of the protochlorophyll(ide) pool of cucumber cotyledons was probed with the use of several [14C]tetrapyrroles in vitro. A comparison of the ratio (R) of delta-amino[14C]levulinic acid incorporation into protochlorophyllide/14C incorporation into protochlorophyllide ester with other incorporation ratios, RX, where X represents any of several [14C]tetrapyrrole substrates, allowed us to determine which exogenous 14C-labeled substrate was common precursor of protochlorophyllide and protochlorophyllide ester and which one was not. From such comparisons, a biosynthetic pathway of protochlorophyll(ide) biosynthesis is inferred. According to this pathway, protochlorophyllide is formed via an acidic (mono/dicarboxylic) biosynthetic branch, while protochlorophyllide ester is formed via a fully esterified (neutral) biosynthetic branch. The two biosynthetic branches are linked together by porphyrin ester synthetases at the level of protochlorophyllides and possibly at the level of the photoporphyrin IX and the magnesium protoporphyrin monoester pools.
利用几种[14C]四吡咯在体外探究了黄瓜子叶原叶绿素（酸）池生物合成过程中两条平行生物合成途径的运作情况。通过比较δ-氨基[14C]乙酰丙酸掺入原叶绿素酸的比例（R）与[14C]掺入原叶绿素酸酯的比例，以及其他掺入比例RX（其中X代表几种[14C]四吡咯底物中的任何一种），我们得以确定哪种外源14C标记底物是原叶绿素酸和原叶绿素酸酯的共同前体，哪种不是。通过此类比较，推断出了原叶绿素（酸）生物合成的一条生物合成途径。根据该途径，原叶绿素酸是通过酸性（单/二羧酸）生物合成分支形成的，而原叶绿素酸酯是通过完全酯化（中性）生物合成分支形成的。这两条生物合成分支在原叶绿素酸水平上，可能还在光卟啉IX和镁原卟啉单酯池水平上，由卟啉酯合成酶连接在一起。
