Page 88 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-06
Enzymes of polyphosphate biosynthesis and degradation
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Biosynthesis of glycoproteins

low Mg 2+
Dol-P P i Dol-PP

high Mg 2+
PolyP n + 1 PolyP n
Figure 6.4 Two possible pathways for dolichyl diphosphate dephosphorylation in yeast cells: Dol-
PP, dolichyl diphosphate; Dol-P, dolichyl phosphate.

GDPMan

GMP

Dol-PP-Man

(Man) n Dol-P

(Man) n + 1

Dol-PP

PolyP n

PolyP n + 1

Figure 6.5 The tentative coupling of PolyP and mannan biosynthesis in yeast: Dol-PP, dolichyl
diphosphate; Dol-P, dolichyl phosphate; GDPMan, GDP mannose; Dol-PP-Man, dolichyl diphosphate
mannose; (Man) n , mannan, where n is the number of mannose residues.

dolichyl-diphosphate:phosphohydrolase activity, which was, however, inhibited by divalent
metal cations. Thus, depending on the divalent metal cations, two pathways of dolichyl
diphosphate dephosphorylation may occur in some yeast cell membranes (Figure 6.4). The
coupling of mannan and PolyP biosynthesis was proposed (Figure 6.5). However, no genetic
data on this enzyme are available.