Regional Distribution of Homocysteine in the Mammalian Brain

The regional distribution of L-homocysteine (Hcy) was determined in brains from mouse, rat, guinea pig, and rabbit, using a sensitive radioenzymatic assay. Large interspecies variations in the Hcy content in various parts of the brain were observed, but cerebellum contained the highest amount in all species investigated. In the rat the amount of Hcy in cerebellum (6.4 nmol/g) was about sixfold higher than in most other parts of the brain, whereas in the mouse and guinea pig the amount in cerebellum (about 1 nmol/g) was only twofold higher than in the other brain regions. There was a remarkably high level of Hcy in all regions of the rabbit brain (4-10 nmol/g); the highest concentration was found in the cerebellar white matter. In this species the amount of Hcy in all brain regions examined exceeded that in the liver.     

Theoretical effects of transmembrane electroneutral exchange on membrane potential

Transmembrane electroneutral transport mechanisms [e.g., Na/H exchange, Cl/HCO3 exchange, (K + Cl) cotransport] have recently been identified in a wide variety of cell types. If these exchanges sum to give a net electroneutral Na/K exchange, they may hyperpolarize the membrane potential beyond the value calculated from the Mullins-Noda equation, provided the cell maintains steady state intracellular ionic concentrations. In extreme circumstances, the membrane potential could hyperpolarize beyond the potassium reversal potential. This effect is mediated by the electrogenic Na/K pump. If either Na or K exchanges electroneutrally against a third ion (e.g., Na/Ca exchange), then the exchange may depolarize the membrane potential.     

Sequence specific antibodies to a deoxyribodinucleotide

Antibodies were elicited in rabbits to the dinucleotide, dpTpA, conjugated to a carrier protein. Among a few deoxyribomono- and oligonucleotides tested for binding to the antibodies by nitrocellulose tilter binding assay, only dpTpA and dpTpA containing oligonucleotides showed binding. The inhibition of the binding of 3H-dpTpA to the antibodies by various nonradioactive mono- and oligonucleotides showed that the antibodies were sequence specific and recognized the whole molecule of dpTpA. dpTpA specific antibodies were purified by a two step affinity chromatography. By competition studies, it was found that the purified antibodies bound denatured DNA at dpTpA sequences. The antibodies did not bind RNA.     

Heliobacterium chlorum: cell organization and structure

The basic cellular organization of Heliobacterium chlorum is described using the freeze-etching technique. Internal cell membranes have not been observed in most cells, leading to the conclusion that the photosynthetic apparatus of these organisms must be localized in the cell membrane of the bacterium. The two fracture faces of the cell membrane are markedly different. The cytoplasmic (PF) face is covered with densely packed particles averaging 8 nm in diameter, while the exoplasmic (EF) face contains far fewer particles, averaging approximately 10 nm in diameter. Although a few differentiated regions were noted within these fracture faces, the overall appearance of the cell membrane was remarkably uniform. The Heliobacterium chlorum cell wall is a strikingly regular structure, composed of repeating subunits arranged in a rectangular pattern at a spacing of 11 nm in either direction. We have isolated cell wall fragments by brief sonication in distilled water, and visualized the cell wall structure by negative staining as well as deep-etching.Abbreviations PF protoplasmic fracture face - EF exoplasmic fracture face     

Tissue uptake of circulating hyaluronic acid

Previous work in the rabbit has shown that there is a significant flux of plasma hyaluronic acid (HA) which is taken up and degraded mainly in the liver but also concentrated in the spleen. Purified 14C-labelled HA of high average molecular wt prepared by biosynthesis from D-[U-14C] glucose was injected i.v. in mice and its tissue distribution was determined by whole-body autoradiography during the next 24 h. As blood levels declined, radioactivity was concentrated in the liver and spleen as found in the rabbit, and also in bone marrow and lymph nodes. Distribution was uniform in liver tissue, concentrated and relatively persistent in the periphery of lymph nodes, and distinctly nodular within the spleen. Analysis of an aqueous liver extract taken 4 h after injection identified 14C in HA, in a macromolecular fraction resistant to fungal hyaluronidase, and in metabolites of low molecular wt. These findings confirm and extend observations based on tissue extraction in rabbits. The pattern of distribution through the body and the restricted localization within spleen and lymph nodes further suggest that HA is absorbed from plasma and tissue fluids by elements of the reticuloendothelial system.     

Differential size variations between transcriptionally active and inactive telomeres of Trypanosoma brucei

We have studied the genes coding for the variant-specific surface antigen (VSA) in a series of seven trypanosome clones derived from AnTat 1.1: 1.1 leads to 1.3 leads to 1.6 leads to 1.16 leads to 1.1C leads to 1.3B leads to 1.18 These genes are all telomeric (1-5), and their surrounding, although sometimes similar, differs in each case. The length between these antigen genes and the corresponding DNA end appears to increase at each antigenic switch, with however occasional sharp size reductions, often linked to the involvement of the telomere in gene expression. This increase is due to a constant "growth" of the telomeres, at a rate of about 28 bp per day in at least four cases and probably linked to chromosome duplication. The telomere harbouring the transcribed VSA gene is growing slightly faster (about 36 bp per day), and it is the only one whose size reduction is progressive, leading to a terminal length heterogeneity within a clone. As a result, the active VSA gene is found in a population of telomeres which, as the trypanosomes divide, becomes increasingly heterogeneous, with however a preferred discrete size class about 1.4 kb smaller. The fact that the "active" telomere is the only one in a chromatin conformation highly sensitive to DNAaseI (1-4, 6), suggests that chromatin structure influences the rate and extent of both size increase and shortening of telomeres.