Journal of Lipid Research, Vol 16, 235-243, Copyright © 1975 by Lipid Research, Inc.
Enzymatic synthesis of mannosyl retinyl phosphate from retinyl phosphate and guanosine diphosphate mannose
GC Rosso, L De Luca, CD Warren and G Wolf
A study was conducted to determine whether retinyl phosphate would act as
substrate for the enzymatic synthesis of mannosyl retinyl phosphate.
Retinyl phosphate, prepared chemically, supported the growth of vitamin
A-deficient rats at the same rate as retinol. It also stimulated the uptake
of [14C]mannose from GDP-[14C]mannose into total chloroform- methanol
extractable lipid. This reaction occurred in the presence of ATP, Mn2+,
detergent (Zonyl A), and a membrane-rich enzyme preparation from the livers
of vitamin A-deficient rats, provided that a lipid extract of the membrane
preparation of alpha-L-lecithin was also added. Total
chloroform-methanol-extractable, labeled mannolipid was separated into two
principal labeled mannolipids by thin-layer or column chromatography or by
differential solvent extraction. The properties of these mannolipids
identified them as glycophospholipids: one was identical with authentic
synthetic dolichyl mannosyl phosphate, and the other was concluded to be
mannosyl retinyl phosphate because of its incorporation of radioactivity
from [3H]retinyl phosphate, its rapid hydrolysis by dilute acid, and the
formation of substance that cochromatographed with retinol upon its acid
hydrolysis. The presence of ATP or GTP was essential for the stimulation of
mannolipid synthesis, probably because of their protective action on the
substrates against phosphatases present in the crude enzyme fraction. A pH
of 6.0-6.2 favored the formation of dolichyl mannosyl phosphate; a higher
pH (6.7-7.0) that of mannosyl retinyl phosphate.
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