References: http://www.utoronto.ca/forest/termite/Decompiculture/Decompiculture/LECTURE3.htm
Decomposition and Recycling of Wood and Wood Products
FOR 1750
Lecture 3 - Jan 25, 1995
Lignin Decomposition and Production Ecology of Wood
Q. What parts of the cell wall contain lignin and what layers contain the most lignin?
Q. What elements make up lignin?
A. CHO no nitrogen, sulfur, phosphate, thus looks similar to carbohydrates, oxidized hydrocarbons, not protein, not lipid, not nucleic acid
Q. What are the basic units making up lignin
phenol propanol with methoxy moeities
Q. What are the starting materials to make these units in lignin biosynthesis?
A. shikimic acid (phenol monosaccharide) to phenalanine (amino acid), cinnamic acid (deaminated unsatuated phenol propane acid) to hydroxycinnamic acid, to caffeic acid (dihydroxy) to ferulic acid (methoxylation) to coniferyl alcohol and peroxidatino to lignin (see Fig. 4.1)
Q. How are the phenol propanol units polymerized?
by peroxidases, resulting many complex reactions involved, covalent bonds (see lignin structure Fig. 4.5)/
Q. Why is lignin recalcitrant to degradation?
Q. What are the main organisms cabable of degrading lignin?
white rot fungi most famous being turkey tail, thin crustlike fungus with brown bands, grows mainly on hardwood logs, very common (P. versicolor = Coriolus versicolor) and bacteria
Q. Why is lignin more difficult to enzymatically decompose than cellulose?
because it is conformationally complex it would take lots of enzymes. Enzymes depend on stereospecific formation, even isomeric specificity. Therefore lignin is partially achieved by non enzymatic, non sterospecific random strong oxidation by peroxide producing organisms.
Q. Compare and contrast lignin and the polysaccharides.
polysaccharides are linear or branches linear polymers, adjacent strands have hydrogen bonds, strands give longitudinal orientation and give strength, lignin is three dimensional trather than 2 dimensional, bonds are diverse, conformation is diverse, good binder (glue-like) but brittle, tends to fracture. In combination lignocellulose is rather similar to fibre glass (polysaccharides = fibers) (lignin = glass) = nature's fibreglass.
Q. What kinds of enzymes are involved in lignin degradation
liginase (general term) cataktse the breakdown of intermonomeric linkages
oxygenases, peroxidases (peroxide producing)
lignin peroxidase, containns an iron poryphrin prosthetic group
laccase (also a peroxide producing enzyme) containing copper and catalyzing the oxidation of p-diphenol to p-benzoquinone in presence of dioxygen O2
Q. What kind of cofactors are used by these enzymes?
iron porphyrin and manganese, Mn-peroxidase
Q. What are some of the intermediate breakdown products?
dimers and monomers
Q. Where does veratry alcohol come in?
It is one of the common products of lignin peroxidase, dimethoxy phenylmethanol 
Q. What are the enzymes that cleave the ring structure?
Q.
Q. What are the ultimate breakdown products?
A. presumably it totally breaks down eventually to CO2 H2O giving heat and ATP
Q. What is the residue?
A. Since it is recalcitrant and takes longer to breakdown in remains in the organic litter layer of the soil longer and there may be organic products that accumulate.
Q. What does phenylalanine metabolism have to do with lignin?
Q. Can lignin be thought of as plant feces? (deaminated fecal sludge)
Q. What are some of the uses of lignin?
Phenolic compounds such as the glues used in plywood.
