PHENYLALANINE HYDROXYLASE FROM SPINACH LEAVES,
Abstract
Spinach leaves contain an enzyme system which catalyses the hydroxylation of L-beta-phenylalanine to tyrosine. The crude active extract has been partially purified by fractional precipitation with acetone, adsorption on DEAE-cellulose, and with calcium phosphate gel. Such preparations showed a 66-fold increase in specific activity. The optimum pH of the reaction was at 4.2. Only L-phenylalanine and L-p-fluorophenylalanine among the compounds tested were substrates of the enzyme system and each was converted to tyrosine. Cinnamic acid was not hydroxylated. No requirement for metal ions could be demonstrated. The partially purified system showed an absolute requirement for electron donors which was satisfied by adding tetrahydrofolic acid and a reduced pyridine nucleotide. The latter could be replaced by ascorbic acid, and the former by an extract of spinach leaves. The active factor in the extract was not obtained pure but behaved as expected for a pteridine derivative during fractionation. The enzyme system was inhibited by concentrations of L-phenylalanine above 1000 M. Aminopterin, cinnamic acid, p-chloromercuribenzoate and sulfhydryl-containing compounds also inhibited the reaction. A kinetic study suggested that the enzyme system from spinach which hydroxylates phenylalanine is similar to that isolated from animal liver. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 08, 1964
- Accession Number
- AD0618161
Entities
People
- L. C. Vining
- P. M. Nair
Organizations
- National Research Council Canada