The formation of homogentisate in the biosynthesis of tocopherol and plastoquinone in spinach chloroplasts

Abstract

Abstract.Homogentisate is the precursor in the biosynthesis of ~-tocopherol and plastoquinone-9 in chloroplasts. It is formed of 4-hydroxyphenylpyruvate of the shikimate pathway by the 4-hydroxyphenylpyruvate dioxygenase. In experiments with spinach the dioxygenase was shown to be localized predominatedly in the chloroplasts. Envelope membranes exhibit the highest specific activity, however, because of the high stromal portion of chloroplasts, 60-80% of the total activity is housed in the stroma. The incorporation of 4-hydroxyphenylpyruvate into 2-methyl-6-phytylquinol as the first intermediate in the tocopherol synthesis by the two-step-reaction: 4-Hydroxyphenylpyruvate ~ Homogentisate Phytyl-PP 2-Methyl-6-phytylquinol was demonstrated by using envelope membranes. Homogentisate originates directly from 4-hydroxyphenylpyruvate of the shikimate pathway. Additionally, a bypass exists in chloroplasts which forms 4-hydroxyphenylpyruvate from tyrosine by an L-amino-acid oxidase of the thylakoids and in peroxisomes by a transaminase reaction. Former results about the dioxygenase in peroxisomes were verified.

Inhibition of Barnyardgrass 4-Hydroxyphenylpyruvate Dioxygenase by Sulcotrione

“…Whereas other investigators have relied solely on spectrophotometric or C 0 2 -capture assays to study HPPD, the present report confirms the existence of HPPD in plants and demonstrates the effect of inhibitors on HPPD activity via methods that simultaneously measure the depletion of substrate and accumulation of product. Previous studies have only implicated the existence of HPPD in plants through substrate-feeding experiments (Loffelhardt and Kindl, 1979;Fiedler et al, 1982). Schulz et al (1993), using TLC, showed that sulcotrione inhibited the formation of HA in rat liver extracts but did not demonstrate the effect on HA formation in plant extracts.…”

The Crystal Structures of Zea mays and Arabidopsis 4-Hydroxyphenylpyruvate Dioxygenase

“…These residues may serve as subcellular targeting signals, e.g. chloroplast import signal as HPPD could contribute to both anabolic synthesis of prenylquinones in chloroplasts and to catabolism of aromatic amino acids in the cytosol (Fiedler et al, 1982). The subcellular localization and the existence of isoforms of HPPD in the plant cell have not been investigated extensively.…”

Broad 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor Herbicide Tolerance in Soybean with an Optimized Enzyme and Expression Cassette

“…Data regarding the subcellular location of HPPD are ambiguous, perhaps resulting from species diversity. Early work with organelle fractions attributed most HPPD activity to the chloroplast in spinach (Spinacia oleracea; Fiedler et al, 1982) or Lemna gibba (Löffelhardt and Kindl, 1979). Organelle targeting can be conjectured from the observation that the N-terminal sequence of mature HPPD isolated from maize leaf begins at either Ala-17 (Fritze et al, 2004) or Ala-23 (Yang et al, 2004) with respect to the translated full-length gene.…”