Scurvy is a disease that until the nineteenth century was common among sailors and others whose diets were deficient in vitamin
C (ascorbic acid). Individuals with scurvy suffer from various disorders, including extensive bruising, hemorrhages, and breakdown of supporting tissues. Ascorbic acid serves as a reducing agent responsible for maintaining the activity of prolyl hydroxylase, the enzyme that catalyzes hydroxylation of proline residues within the collagen triple helix, which is required for helix stability. (a) Based on this information, postulate a role for hydroxyproline in collagen triple helices, and explain the sequence of events leading from a dietary vitamin C deficiency to symptoms such as bruising and breakdown of supporting tissues.
(b) Can you guess why sailors are no longer susceptible to scurvy? Why are British sailors called "limeys" to this day?
(a) Collagen is the major structural component of cartilage,bones and tendons
The basic unit of collagen is tropocollagen and each tropocollagen consists of three coiled left handed polypeptide chains called α chains
Generally each α chain consists of a repeating tripeptide sequence called: G-X-Y
Here G represents glycine; X represents proline and Y represents hydroxyproline
Rigidity of collagen molecule is due to presence of proline and hydroxyproline
Hydroxylation of proline is catalysed by prolyl hydroxylase enzyme which use ascorbate,α ketoglutarate and oxygen
α ketoglutarate is oxidatively decarboxylated to form carbon dioxide and succinate
Sequence of events leading from a dietary vitamin C deficiency to symptoms such as bruising and breakdown of supporting tissues includes:tissue levels of ascorbic acid is low; enzyme prolyl hydroxylase is inactive;proline is not hydroxylated; the triple helix is inadequately stabilized; collagen breaks down; defects in tissues that depend on collagen
; tissues that depend on collagen are subject to breakdown and bruising
(b) Sailors are no longer susceptible to scurvy because fresh fruits which are the source of vitamin C source are available now
British sailors called "limeys" to this day,this term reflects the British navy's use of limes
