title: Functional studies of rat hydroxymethylbilane synthase.
abstract: The structurally related tetrapyrrolic pigments are a group of natural products that participate in many of the fundamental biosynthetic and catabolic processes of living organisms. Hydroxymethylbilane synthase catalyzes a rate-limiting step for the biosyntheses of tetrapyrrolic natural products. We carried out extensive studies of rat hydroxymethylbilane synthase in the present investigation. The enzymatic reaction rate of the holoenzyme was found to be lower than those of the enzyme-intermediate complexes, which corrected the previous theoretical analysis result. Several mutants were constructed, purified and characterized. D44 was found to play an important role in the disassembly of the enzyme-intermediate complexes. E63 and H78 were important for maintaining the activity of the enzyme at high temperature. Four substrate analogs with variation of porphobilinogen side-chain were synthesized and incubated with the enzyme. Three analogs were found to be weak substrates of the enzyme. All four analogs can be used for the preparation of uroporphyrin I analogs.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, PR China.
authors.forename: Nan
authors.initials: N
authors.lastname: Li
authors.forename: Xiusheng
authors.initials: X
authors.lastname: Chu
authors.forename: Long
authors.initials: L
authors.lastname: Wu
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Liu
authors.forename: Ding
authors.initials: D
authors.lastname: Li