Mannosyl retinyl phosphate

Rosso, G., DeLuca, L., Warren, C.D. Wolf, G. (1975) Enzymatic Synthesis of Mannosyl Retinyl Phosphate from Retinyl Phosphate and Guanosine Diphosphate Mannose , Journal of Lipid Research, 16, 235-43... 

Rosso, G.C., Masushige, S., Quill, H. Wolf, G. (1977) Transfer of Mannose from Mannosyl Retinyl Phosphate to Protein , Proceedings of the National Academy of Sciences, USA, 74, 3762-6... 

Rosso, G.C., Masushige, S., Warren, C.D., Kiorpes, T. Wolf, G. (1976) The Anomeric Configuration of the D-Mannosyl Retinyl Phosphate Formed in Rat Liver Microsomes , Journal of Biological Chemistry, 251, 6465-7 Rubery, P.H. Northcote, D.H. (1970) The Effect of Auxin (2,4-dichloro-phenoxyacetic Acid) on the Synthesis of Cell Wall Polysaccharides in Cultured Sycamore Cells , Biochimica et Biophysica Acta, 222, 95-108... 

A13 Retinyl mannosyl hydrogen phosphate [61152-15-6] Mannosyl retinyl phosphate Retinyl p-D-mannopyranosyl hydrogen phosphate... 

Retinyl phosphate has been shown to be formed in mammalian cells both in vitro and in vivo and has been identified as a trace constitutent of certain mammalian membranes. Its glycosylated derivative mannosyl retinyl phosphate has also been shown to be formed both in vivo and in vitro. The enzyme system that forms mannosyl retinyl phosphate is located primarily in the rough endoplasmic reticulum of rat liver cells. Under appropriate conditions, glycosyl transfer can be demonstrated from the retinyl glycolipid to membrane glycoproteins. It is not known, however, whether this occurs in vivo under normal conditions. 

In the synthesis of most glycoproteins containing mannose, the intermediate carrier of the mannosyl moiety is the polyene dolichol phosphate. However, in some systems, retinyl phosphate can act as the intermediate carrier between UDP-mannose and the acceptor glycoprotein. Retinyl phosphate maimose seems to be involved especially in the synthesis of hydrophobic regions of glycoproteins (DeLuca, 1977 Frot-Coutaz et al., 1985). 

Frot-Coutaz, Silverman-Jones and De Luca (1976) confirmed that retinol could be converted into retinyl phosphate by intact cells. Hamster intestinal epithelium was used and the product was characterised by a variety of partition and ion-exchange chromatographic procedures and by chemical comparison with an authentic (synthetic) sample of retinyl phosphate. Hence all the steps necessary for the synthesis of retinyl mannosyl phosphate from retinol could be demonstrated in the whole cell. 

What is the physiological role — if any — of retinyl mannosyl phosphate Does it act as a mannosyl donor in glycopeptide assembly There is no simple answer as yet. It is clearly established that many cells can synthesise retinyl phosphate from retinol and, thence, can produce retinyl mannosyl phosphate, so the substance itself is clearly a physiological product. 

Martin and Thorne (1974) showed that microsomes from rat liver could synthesise both retinyl mannosyl phosphate and dolichyl mannosyl phosphate in vitro and with comparable efficiency, and Rosso et al (1975) found that retinol phosphate would stimulate retinyl mannosyl phosphate synthesis from GDP [ Man in a similar system, if ATP,Mn and lipid extract were added. 

De Luca (1977b) later showed that retinyl mannosyl phosphate was produced in vivo, by injecting [ " Cjretinol into hamsters made deficient in vitamin A. On the other hand, mevalonic acid is a precursor of dolichol and can be used, selectively, to label it in vivo. 

In summary, retinyl mannosyl phosphate has the P-anomeric configuration, like the dolichyl mannosyl phosphate, since it yielded mannose-2-phosphate upon mild alkaline cleavage (Rosso et al, 1976). Its properties... 

A possible transfer of mannose from retinyl mannosyl phosphate to polypeptide was first indicated by the studies of Maestri and De Luca (1973), though these did not prove that retinyl mannosyl phosphate was the mannosyl donor. In a more detailed analysis Rosso etaL (1977) used a radioactive label largely free of dolichyl mannosyl phosphate in a cell-free system and obtained a clear-cut incorporation of mannose from retinyl mannosyl phosphate into a substance with the solubility properties of protein and which was labile to proteolysis. Some free mannose, its 1-phosphate and retinyl mannosyl phosphate were also present at the end of the incubation, but no large mannolipid was detected. Dolichy CJmannosyl phosphate did not give any transfer of [ C] mannose to protein and further support for a distinctive retinol pathway came from the effects of EDTA. This totally failed to block transfer from retinyl [ mannosyl phosphate, under conditions where block... 

---