The chemistry of the bioluminescence of the New Zealand Glow-Worm

Abstract

The aim of the research described in this thesis was to discover the luciferin responsible for bioluminescence in the New Zealand glow-worm (GW) Arachnocampa luminosa. This work was done in partnership with Dr Miriam Sharpe whose focus was to elucidate the luciferase. In order to determine the structure of the GW luciferin, the luciferin had to be isolated from the GW and the structure elucidated via characterisation. However, luciferin purifications pose a unique isolation challenge, combining the difficulties of isolating material from source organisms, working with unstable materials, and working with enzymatic assays. Furthermore characterisation of luciferins is often difficult due to the small amounts that can be isolated and because luciferins are often highly unstable. Previous work on luciferins in other organisms and on the GW luciferin is reveiwed in Chapter 1. Chapter 1 also reviews the general literature on bioluminescence but with a focus on luciferins rather than luciferases.

Chapters 2 describes the collection of Arachnocampa luminosa from the wild, and the development of a GW bioluminescence assay that enabled GW luminescent molecules to be detected. This assay enabled the detection of two different types of luminescence: P type luminescence and L type luminescence. Chapter 3 describes the separation of glow-worm lysates by reverse phase chromatography and how the luminescence assay was used to trace GW luminescent molecules through the purification process. This led to the discovery of two glow-worm luciferin precursors: tyrosine and xanthurenic acid that gave P type luminescence with the GW bioluminescence assay. The compound responsible for the L type luminescence was separated away from the compounds responsible for P type luminescence but could not be isolated. The compound responsible for L type luminescence was found to co-elute with tryptophan and is thought to be the GW luciferin.

Chapter 4 describes how commercial samples of these precursors (xanthurenic acid and tyrosine), along with GW enzymes, were used to produce a compound (LRPA) that could be characterised by MS and 1H NMR. A solution of LRPA was found to produce L type luminescence with the luminescence assay showing LRPA to be either the GW luciferin or a closely related compound.

Chapter 5 then describes the synthesis of two molecules (N-carbamyl tyrosine and phenol-O-carbamyl tyrosine) that were candidates for a compound that co-eluted with tyrosine. Neither of these molecules matched the unknown candidate which was later found to be 3-OH kynurenine.

The research on the New Zealand glow-worm described in this thesis required intensive use of LC-MS techniques. However the research was often slowed by a shortage of glow-worms. These techniques were therefore used to investigate another New Zealand natural products problem involving insect metabolites; the origins of tutin, hyenanchin and the tutin glucosides found in New Zealand toxic honeys. Chapter 6 therefore describes a quantitative LC-MS study that shows that these compounds are of plant, not insect origin and that tutu may use glycosylation to aid in tutu transport.