An Evaporimeter and a ventilated chamber technique have been compared in their ability to measure transepidermal water loss (TEWL) through rat skin. These techniques measure TEWL under very different conditions; the Evaporimeter measures the net TEWL under ambient relative humidity (RH) whereas the ventilated chamber employs a constant atmosphere, usually of low RH and thus measured the uni-directional diffusion of water. Paired Evaporimeter and ventilated chamber measurements were made of TEWL through normal skin and through skin whose barrier properties had been altered by tape-stripping (15 applications) or single applications of n-hexadecane (28.4 mumol cm-2). Both measuring techniques indicated the same level of TEWL through normal skin (mean 0.3 mg cm-2 h-1) and during increases in TEWL induced by n-hexadecane (max TEWL c 3.5 mg cm-2 h-1). However, the Evaporimeter was found to underestimate the higher rates of TEWL induced by tape-stripping, ie above TEWL raters of 7.5 mg cm-2 h-1. The Evaporimeter is portable, easy to use and suitable for measurements of net water loss up to 7.5 mg cm-2 h-1; it can only be used for comparative assessment of epidermal barrier function if used at a particular ambient RH. The more cumbersome ventilated chamber is to be preferred for accurate assessments of barrier function where high rates of TEWL occur.
In the chain-lengthening of the oligosaccharide chains of endogenous dolichol-diphosphate oligosaccharides (Dol-P-P-oligosaccharides) by a pig liver microsomal preparation dolicholmonophosphate mannose (Dol-P-Man) was a more efficient donor of mannose (a maximum of 35 SC transferred by 5 min) than was GDP-Man (reaching 16 7; by 45 min). The effects of an excess of GDP, an excess of GDP-Man, a lack of Mn" and an excess of EDTA showed that the transfer from GDP-Man was via Dol-P-Man. The evidence also indicated the presence of two pools of Dol-P-Man one of which was difficult to extract and which was possibly closely associated with the Dol-P-P-oligosaccharides and the appropriate transferase.After 1 h of incubation transfer of '"C to 'insoluble polymer' from GDP-[14C]Man, Dol-P-[I4C]Man and Dol-P-P-['4C]~ligo~accharide~ reached approximately 3 x, 3 % and 13 % respectively, of that available. The result of adding excess unlabelled GDP-Man to an incubation with GDP-['"CIMan in progress confirmed the sequence GDP-Man + Dol-P-Man + Dol-P-P-oligosaccharide + insoluble polymer. Solubilisation with sodium dodecyl sulphate of the radioactive 'insoluble polymer' followed by gel chromatography showed the presence of radioactive glycoprotein and oligosaccharide when either GDP-['"CIMan or Dol-P-P-['4C]oligosaccharide was used as donor. The proportion of oligosaccharide formed rose sharply when excess EDTA was present and GDP-['"C]Man was the donor. Under these conditions the oligosaccharide contained 5-6 units and all of the radioactivity could be released by a-mannosidase. The glycoprotein was susceptible to proteolysis.When GDP-['"CIMan is incubated with microsoma1 preparations of various tissues [14C]mannose is transferred to dolichol monophosphate (Dol-P) and to dolichol-diphosphate (Dol-P-P) oligosaccharides [l -41. In the case of the pig liver system it has been shown that the oligosaccharide portion of the Dol-P-P-['"C]oligosaccharides so formed ranges in chain length from approximately seven to 13 sugar residues and that these are formed generally by addition of one mannose residue to the oligosaccharide chain of each endogenous Dol-P-P-oligosaccharide with a minority being formed by addition of two mannose residues [4]. It was of interest to determine if the dolichol-phosphate-['"C]mannose (Do~-P-['~C]-Ahhreviationu. Dol-P-Man, dolichol-monophosphate-mannose ; Dol-P-P-oligosaccharides, dolichnl-diphosphatc-oligosaccharides; GDP-Man, guanosinr-diphosphate-mannose. Man) formed in this system could act as a direct donor of mannose residues in the chain-lengthening of endogenous Dol-P-P-oligosaccharides and the results of experiments to this end are described in this paper. . We also report here on the relationships between the lipid-linked compounds and the formation of glycoprotein and oligosaccharide in the pig liver system.
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