Xantha-l encodes a membrane subunit of the aerobic Mg-protoporphyrin IX monomethyl ester cyclase involved in chlorophyll biosynthesis

Research output: Contribution to journalArticle

Abstract

Chlorophyll biosynthesis is a process involving approximate to 20 different enzymatic steps. Half of these steps are common to the biosynthesis of other tetrapyrroles, such as heme. one of the least understood enzymatic steps is formation of the isocyclic ring, which is a characteristic feature of all (bacterio)chlorophyll molecules. In chloroplasts, formation of the isocyclic ring is an aerobic reaction catalyzed by Mg-protoporphyrin IX monomethyl ester cyclase. An in vitro assay for the aerobic cyclase reaction required membrane-bound and soluble components from the chloroplasts. Extracts from barley (Hordeum vulgare Q mutants at the Xantha-1 and Viridis-k loci showed no cyclase activity. Fractionation of isolated plastids by Percoll gradient centrifugation showed that xantha-1 and viridis-k mutants are defective in components associated with chloroplast membranes. The Xantha-1 gene, corresponding to Arabidopsis thaliana CHL27, Rubrivivax gelatinosus acsF, Chlamydomonas reinhardtii CRD1, and CTH1 and situated at the short arm of barley chromosome 3 (3H), was cloned, and the mutations in xantha-l(35), xantha-l(81), and xantha-l(82) were characterized. This finding connected biochemical and genetic data because it demonstrated that Xantha-1 encodes a membrane-bound cyclase subunit. The evidence suggests that the aerobic cyclase requires at least one soluble and two membrane-bound components.

Details

Authors
  • Kamila Rzeznicka
  • C J Walker
  • Tomas Westergren
  • C G Kannangara
  • D von Wettstein
  • S Merchant
  • Simon Gough
  • Mats Hansson
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences
Original languageEnglish
Pages (from-to)5886-5891
JournalProceedings of the National Academy of Sciences
Volume102
Issue number16
Publication statusPublished - 2005
Publication categoryResearch
Peer-reviewedYes