Chemical structures in a lignin-carbohydrate complex isolated from the bovine rumen

The soluble, lignin-carbohydrate complex (LCC) from the rumen fluid of steers fed a diet of pure spear grass (Heteropogon contortus) has been purified by gel filtration. The purified LCC contained 7.4% of carbohydrate which, on hydrolysis, gave d-glucose, d-xylose, l-arabinose, l-rhamnose, and traces of d-galactose and d-mannose. The structure of the LCC was examined by methylation analysis, using g.l.c.-m.s. for the unequivocal classification of the sugar derivatives. d-Glucose, d-xylose, and l-rhamnose were shown to be glycosidically linked to lignin. Some of the d-glucosyl residues carry other (1→4)-linked d-glucose units, and some of the d-xylosyl residues bear other (1→4)-linked d-xylose units and (1→3)-linked l-arabinofuranosyl groups. The major carbohydrate component is a single d-glucopyranosyl group. The LCC was subjected to various chemical treatments in an investigation of the chemical nature of the bonding between lignin and the carbohydrates. d-Glucose could be enzymically hydrolyzed from the LCC, but only with a very high concentration of β-d-glucosidase. The presence of lignin in rumen LCC has been confirmed by nitrobenzene oxidation, vanillin and syringaldehyde being identified by g.l.c.-m.s. as oxidation products from both the original spear grass and the LCC.     

An Unexpected Major Groove Binding of Netropsin and Distamycin A to tRNAphe

Abstract

Crystalline complexes of yeast tRNA^phe and the oligopeptide antibiotics netropsin and distamycin A were prepared by diffusing drugs into crystals of tRNA. X-ray structure analyses of these complexes reveal a single common binding site for both drugs which is located in the major or deep groove of the tRNA T-stem. The netropsin-tRNA complex is stabilized by specific hydrogen bonds between the amide groups of the drug and the tRNA bases G51 0(6), U52 0(4) and G53 N(7) on one strand, and is further stabilized by electrostatic interactions between the positively charges guanidino side chain of the drug and the tRNA phosphate P53 on the same strand and the positively charged amidino propyl side chain and the phosphates P61, P62 and P63 on the opposite strand of the double helix. These results are in contrast to the implicated minor groove binding of these drugs to non-guanine sequences in DNA. The binding to the GUG sequence in tRNA implies that major groove binding to certain DNA sequences is possible.     

DNA replication stress: Causes,resolution and disease

DNA replication is a fundamental process of the cell that ensures accurate duplication of the genetic information and subsequent transfer to daughter cells. Various pertubations, originating from endogenous or exogenous sources, can interfere with proper progression and completion of the replication process, thus threatening genome integrity. Coordinated regulation of replication and the DNA damage response is therefore fundamental to counteract these challenges and ensure accurate synthesis of the genetic material under conditions of replication stress. In this review, we summarize the main sources of replication stress and the DNA damage signaling pathways that are activated in order to preserve genome integrity during DNA replication. We also discuss the association of replication stress and DNA damage in human disease and future perspectives in the field.     

Analysis of the pinocytic process in rat kidney II. Biochemical composition of pinocytic vesicles compared to brush border microvilli,lysosomes and basolateral plasma membranes

Pinocytic vesicles, brush border microvilli, lysosomes and basolateral plasma membranes were isolated from rat kidney cortex and their biochemical composition and membrane turnover compared. Pinocytic vesicles are devoid of marker enzymes of brush border microvilli, such as alkaline phosphatase and 5′-nucleotidase, and of lysosomes, such as acid phosphatase and β-glucuronidase. The protein pattern as revealed by polyacrylamide gel electrophoresis differs for all four membranes. Analysis of the phospholipid composition shows that pinocytic vesicles are rich in the negatively charged phospholipid phosphatidylserine and have a low content of sphingomyelin and phosphatidylethanolamine.[¹⁴C]guanido-arginine, [³H]fucose and $\text{myo-}\text{[}{}^3\text{H]inositol}$ were preferentially incorporated into the pinocytic vesicles. Using a double label technique with leucine also, evidence of a more rapid turnover of the pinocytic vesicle membrane proteins was obtained.The results suggest that pinocytic vesicles are not derived from the brush border microvillous membrane but are independent entities that are newly synthesized during the pinocytic process.     

Mediation of high-temperature injury by roots and shoots during reproductive growth of wheat

Abstract Previous studies suggest that high temperature stress on wheat (Triticum aestivum L.) involves root processes and acceleration of monocarpic senescence. Physiological changes in wheat roots and shoots were investigated to elucidate their relationship to injury from elevated temperatures after anthesis. Plants were grown under uniform conditions until 10 d after anthesis, when shoot/root regimes of 25°C/25°C, 25°C/35°C, 35°C/25°C and 35°C/35°C were imposed. Growth and senescence of shoots and grain were influenced more by root temperatures than by shoot temperatures. High root temperatures increased activities of protease and RNasc enzymes, and loss of chlorophyll, protein and RNA from shoots, whereas low root temperatures had opposite effects. High root temperatures appeared to induce shoot senescence directly. High shoot temperatures probably disrupted root processes, including export of cytokinins, and induced high leaf protease activity, senescence and cessation of grain development. The authors concluded that responses of wheat to high temperatures, whether of roots or shoots, are manifested as acceleration of senescence and may be mediated by roots during grain development.     

Suppression of endocytosis in polyclonally activated Con A-stimulated T lymphocytes by 25-hydroxycholesterol

A new high quality young-calf serum, Hy-clone calf serum (HcCS), was tested for use in hybridoma culture. This calf serum alone had little growth promoting activity and was much inferior to fetal calf serum (FCS). Red cell lysate (RCL) used in combination with the young-calf serum showed very good growth promoting activity. Growth was increased about threefold over that in the presence of FCS. However, HcCS and RCL could not substitute for feeder cells when hybridomas were cultured as single cells under conditions of limiting dilution. It is thought likely that the potent growth promoting factor in red cell lysate is hemoglobin.