section 11.1
Protein Fibers and Proteoglycans
177
Polypeptide
chain
\y Lysine
residue
KN
Lysyl
oxidase
H.
C'
Aidol
condensation
(-H20)
c= o
O
H
Aidol condensation
product
C'
O
H
O
H
Polypeptide
chain
(a)
Formation of aidol condensation product— linkage involving nonhelical
regions of the collagen molecule.
Polypeptide chain
(helical region)
Polypeptide chain
(nonhelical region)
Dehydro-
hydroxy-
lysino-
norleucine
(b)
Formation ofdehydrohydroxylysinonorleucine linkage.
Polypeptide chain
(helical region)
Polypeptide chain
(nonhelical region)
Polypeptide chains (nonhelical regions)
F orm ation o f dehydrohydroxylysinohydroxynorleucine(I), an aldim ine, and
hydroxylysino-5-keto-norIeucine{II), a ketam ine. T h e linkage in II is m ore
stable.
(d)
F orm ation o f pyridinoline cross-linkage, a polyfunctional cross-linkage.
F IG U R E 1 1 -3
Formation of cross-links in collagen. All cross-links are derived from lysyl and hydroxylysyl amino acid residues. The
initial step is the oxidative deamination of the s-NFU group of two amino acid residues located at certain strategic
positions (e.g., short nonhelical segments at both ends of the collagen molecule), with the formation of corresponding
aldehyde-containing residues, allysine and hydroxyallysine. This reaction occurs extracellularly and is catalyzed by
lysyl oxidase, a copper-dependent enzyme. The aldehyde groups react spontaneously with other aldehyde groups
located in the adjacent chain of the same molecule or adjacent molecule. The structures do not show carbohydrate
moieties for the sake of clarity.
,/ \ /
