Tetrapyrrole biosynthesis in Anacystis nidulans; incorporation of [1-13C]-, [2-13C]-, [1,2-13C]- and [2-13C, 2-2H3]acetate

Labelling experiments with [2-¹³C]- and [1,2-¹³C]acetate showed that both photopigments of Anacystis nidulans, chlorophyll a and phycocyanobilin, share a common biosynthetic pathway from glutamate. The fate of deuterium during these biosynthetic events was studied using [2-¹³C, 2-²H₃]acetate as a precursor and determining the labelling pattern by ¹³C NMR spectroscopy with simultaneous [¹H, ²H]-broadband decoupling. The loss of ²H (ca 20%) from the precursor occurred at an early stage during the tricarboxylic acid cycle. After formation of glutamate there was no further loss of ²H in the assembly of the cyclic tetrapyrrole intermediates or during decarboxylation and modification of the side-chains. Thus the labelling data support a divergence in the pathway to cyclic and linear tetrapyrroles after protoporphyrin IX.