Nicolás H. Behrens

Bio: Nicolás H. Behrens is an academic researcher from Facultad de Ciencias Exactas y Naturales. The author has contributed to research in topics: Dolichol & Mannose. The author has an hindex of 14, co-authored 18 publications receiving 1211 citations.

Dolichol Monophosphate Glucose: An Intermediate in Glucose Transfer in Liver

Abstract: The microsomal fraction of liver has been found to catalyze glucose transfer from UDPG to a lipid acceptor which appears to be identical to the compound obtained by chemical phosphorylation of dolichol. The substance formed (dolichol monophosphate glucose) is acid labile and yields 1,6-anhydroglucosan by alkaline treatment. It can be used as substrate by the enzyme system yielding a glucoprotein which is subsequently hydrolyzed to glucose.

The role of polyprenol-bound saccharides as intermediates in glycoprotein synthesis in liver.

Abstract: It has been reported that liver microsomes catalyze the transfer of glucose from uridine diphosphate glucose to dolichol monophosphate so as to produce dolichol monophosphate glucose. Dolichol is a polyprenol containing about 20 isoprene units. The glucosyl residue of dolichol monophosphate glucose is transferred to an endogenous acceptor on further incubation with liver microsomes. The glucosylated endogenous acceptor appears to be an oligosaccharide of about 20 monosaccharide units bound to dolichol through a phosphate or pyrophosphate bridge. In this paper it is reported that liver microsomes catalyze the transfer of the oligosaccharide from the glucosylated endogenous acceptor to an endogenous protein. This transfer reaction requires the presence of bivalent cations, manganese being more effective than magnesium. The presence of deoxycholate is also required. Besides the glycoprotein, several water-soluble products are also formed. Preliminary evidence indicates that they are glucose, iligosaccharides of different size, and possibly oligosaccharides bound to amino acids.

Glucose Transfer from Dolichol Monophosphate Glucose: The Product Formed with Endogenous Microsomal Acceptor

Abstract: The product formed by incubation of dolichol monophosphate glucose with liver microsomes was studied. It is insoluble in most solvents, but is soluble in a chloroform-methanol mixture with a high content of water. Treatment with ammonia gave rise to the formation of a water soluble, negatively charged compound of molecular weight 3550. The negative charge could be removed by treatment with phosphatase. Acid hydrolysis of the original compound led to the liberation of an uncharged, water-soluble compound (molecular weight 3550). Acetolysis of the latter gave rise to the formation of a series of products, which appeared to be oligosaccharides when chromatographed on paper or silica plates. The original substance behaved like a polyprenol pyrophosphate when chromatographed on DEAE-cellulose. Molecular weight measurements of the deoxycholate inclusion compound gave a value of 14,300, while dolichol monophosphate glucose under the same conditions gave 11,300. It is tentatively suggested that the compound is dolichol joined through a phosphate or pyrophosphate bridge to an oligosaccharide containing about 20 monosaccharide residues.

Formation of Lipid-Bound Oligosaccharides Containing Mannose. Their Role in Glycoprotein Synthesis

Abstract: Incubation of GDP-[14C]mannose with liver microsomes and magnesium ions led to the formation of dolichol monophosphate mannose and of other acidlabile compounds that contain oligosaccharides. Formation of these compounds was enhanced by addition of an acceptor lipid in the same fractions of DEAE-cellulose chromatography where bound dolichol is found. Alkaline treatment of the oligosaccharides, obtained by acid methanolysis, followed by paper electrophoresis, gave rise to the formation of two positively charged substances believed to be formed by deacetylation of hexosamine residues. Incubation of the oligosaccharide-containing compounds with liver microsomes and manganese ions resulted in a transfer to endogenous protein. The role of dolichol derivatives in glycoprotein synthesis is discussed.

Cellular Biology and Biochemistry of the Retinoids

Abstract: Publisher Summary This chapter discusses the cellular biology and biochemistry of the retinoids In isolated 9-day-old rat embryos, retinoic acid prevents the formation of the pharyngeal arches, which are derived from cephalic mesenchyme; these structures later form the maxilla and the mandible Another mesenchymal derivative, whose formation is markedly suppressed by retinoic acid in rat embryos, is the yolk sac circulation Retinoids can exert a powerful influence on cell differentiation in many different types of epithelia The effects of retinoids on differentiation of epithelia in organ culture result from a combination of complex cellular responses and interactions of different cell types in the explant One of the most illuminating examples of the ability of retinoids to promote differentiation is the effect of retinoids on mouse embryonal carcinoma cells These undifferentiated stem cells of teratocarcinomas are multipotential, that is, they can differentiate into a multiplicity of somatic cell types Another example of the ability of retinoic acid to promote terminal differentiation of neoplastic cells to nonneoplastic cell types is the effect of retinoic acid on human promyelocytic leukemia cells

In and Out of the ER: Protein Folding, Quality Control, Degradation, and Related Human Diseases

Abstract: A substantial fraction of eukaryotic gene products are synthesized by ribosomes attached at the cytosolic face of the endoplasmic reticulum (ER) membrane. These polypeptides enter cotranslationally in the ER lumen, which contains resident molecular chaperones and folding factors that assist their maturation. Native proteins are released from the ER lumen and are transported through the secretory pathway to their final intra- or extracellular destination. Folding-defective polypeptides are exported across the ER membrane into the cytosol and destroyed. Cellular and organismal homeostasis relies on a balanced activity of the ER folding, quality control, and degradation machineries as shown by the dozens of human diseases related to defective maturation or disposal of individual polypeptides generated in the ER.