Yeast sterol esters and their relationship to the growth of yeast.

Variation in the percentage of sterols esterified to long-chain fatty acids during cellular growth has been examined. Under all conditions, a constant percentage of sterol esters was maintained during exponential growth. This maintenance level was found to vary with different growth conditions. A sharp increase in the rate of esterification was observed upon entry of the culture into the stationary growth phase. The minor cellular sterol components were found to accumulate after this period of rapid sterol ester synthesis, with a relative decrease in the size of the ergosterol pool. Evidence is presented that sterol esters of ergosterol precursors are unable to be metabolized to ergosterol. Once esterified, the fatty acids do not appear to be scavenged during starvation conditions.     

Chemistry of the collagen cross-links. Nature of the cross-links in the polymorphic forms of dermal collagen during development.

Both the type I and type III collagens present in embryonic dermis are stabilized by the intermolecular cross-link, hydroxylysino-5-oxonorleucine, derived from hydroxylysine-aldehyde, although the type I collagen possesses a significant proportion of dehydrohydroxylysinonorleucine. However, concurrent with the change in the proportion of the two types of collagen during postnatal development there is a change-over with both type I and III collagens to the labile cross-link, dehydrohydroxylysinonorleucine, derived from lysine aldehyde. The results indicate that the change in the nature of the cross-link with development is determined primarily by the change in the extent of hydroxylation of the lysine residues in the terminal non-helical regions rather than being due to the change in the type of collagen.     

Alkali solubility of hemicelluloses in relation to delignification

The polysaccharide composition of bark from Pinus radiata, Salix fragilis, and Populus euramericana has been determined. All the barks contained lower levels of cellulose and hemicellulose than the corresponding woods; cellulose: hemicellulose ratios were also lower in the barks. Alkali extracted all of the hemicellulose-A but only half of the hemicellulose-B from P. radiata bark without prior delignification. Similar alkaline extraction removed almost all of the hemicellulose (A + B) from ryegrass leaves without delignification. With the other samples tested only a part of the hemicellulose A and B is extracted without delignification. It is suggested that the polysaccharide so extracted represents wall hemicellulose which is not linked to lignin or other wall constituents by alkali-stable links.     

Genetics of histocompatibility in mice

Twenty-five new congenic lines with distinctive BALB/cBy-strain histocompatibility alleles introduced onto the C57BL/6By-strain background by a regimen of backcrossing and tailskin grafting have been established. Twenty-one of the histocompatibility loci represented by these lines are new, while four duplicate theH-1, H-2, H-7, andH-8 loci identified by Snell.     

Adhesion of bacteria to epithelial cell surfaces within the reticulo-rumen of cattle

Blocks of tissue were removed from various locations in the bovine digestive tract and fixed and processed for transmission and scanning electron microscopy by techniques that retained adherent bacteria. The distribution of bacteria on the surface of epithelial cells was examined by scanning electron microscopy. This showed intermittent colonization of the epithelia with the formation of occasional microcolonies of morphologically similar bacterial cells. Transmission electron microscopy of ruthenium red-stained material showed the presence of both the glycocalyx of the bovine epithelial cells and fibrous carbohydrate coats surrounding adherent bacteria. The carbohydrate coats appeared to mediate the attachment of bacteria to the epithelium, to food particles, and to each other so that microcolonies were formed. Careful examination of the bacterial colonization of keratinized cells in the process of being sloughed from the surface of the stratified squamous epithelium of the rumen showed that these dead cells were digested by adherent bacteria of a limited number of morphological types. The spatial relationship of this mixed, adherent, microbial population to living and dead epithelial cells and to food particles indicates that digestive processes of some importance may be accomplished by this stationary component of the microbial flora of the digestive tract.     

Reduction of catheter-associated sepsis in parenteral nutrition using low-dose intravenous heparin.

To assess whether adding low-dose heparin to the infusate of patients receiving parenteral nutrition reduced the incidence of septic complications related to the central venous catheter, 80 consecutive patients requiring intravenous feeding were studied. Half of these patients received heparin 1 unit/ml of infusate, while in the remaining 40 (controls) an equal volume of physiological saline was added to the infusate. Strict criteria for the management of the indwelling CVC were observed. The catheter tips were cultured after removal: only one was infected in the heparin group compared with nine in the control group. This significant reduction may have been due to the heparin preventing a fibrin sleeve from forming around the catheter tip. It is recommended that, as well as observing the usual aseptic precautions in managing the cannula, 500 units of heparin are added to each 500 ml of fluid infused to reduce the incidence of catheter-associated sepsis.