Fig. 5

Histidine biosynthetic pathway in robust corals. The biochemical pathway by which histidine is synthesised from phosphoribosyl pyrophosphate is the same in plants, fungi, and bacteria, but some steps are brought about by unrelated proteins in different organisms. In robust corals, a fungal-like complement of enzymes is involved, the proteins responsible being (a) ATP phosphoribosyltransferase, (b) histidine biosynthesis trifunctional protein, (c) 5′ProFAR isomerase, (d) IGP synthase, (e) imidazoleglycerol-phosphate dehydratase, (f) histidinol-phosphate aminotransferase, and (g) histidinol-phosphate phosphatase. Abbreviations used: PRPP, phosphoribosyl pyrophosphate; ATP; adenosine triphosphate; PPi, pyrophosphate; PR-ATP, phosphoribosyl-ATP; PR-AMP, phosphoribosyl-AMP; 5′ProFAR, 1-(5-phosphoribosyl)-5-[(5-phosphoribosylamino) methylideneamino] imidazole-4 carboxamide; PRFAR, 5-[(5-phospho-1-deoxyribulos-1-ylamino)methylideneamino]-1-(5-phosphoribosyl) imidazole-4-carboxamide; IGP, imidazole-glycerol phosphate; AICAR, 1-(5′-phosphoribosyl)-5-amino-4-imidazolecarboxamide; IAP, imidazole-acetol phosphate; Hol-P, L-histidinol phosphate; Pi, phosphate; NAD+, oxidised nicotinamide adenine dinucleotide; NADH, reduced nicotinamide adenine dinucleotide