Rat and human embryo and post-natal sera contain a potent endogenous competitor of estrogen-rat alpha-fetoprotein interactions

A highly active inhibitor of the binding of estrone and estradiol-17β to rat alpha-fetoprotein is demonstrated for the first time in embryo, immature and adult rat sera as well as in fetal and adult human sera. The competitive character and the narrow specificity of this inhibition effect is shown. The major compound responsible for this activity is isolated by successive column Sephadex LH₂₀ and thin layer chromatography : it is characterized as a nonpolar, nonphenolic, dialysable and thermostable substance, unreactive towards anti-estrone and anti-estradiol-17β anti-bodies. The possible biological role of an endogenous non-estrogen ligand of rodent fetoproteins is discussed.     

Grain size,sucrose level and starch accumulation in developing rice grain

Five rices (Oryza sativa L.) differing in final grain size were studied at the midmilky stage to determine if any factor could be identified which might limit rate of starch accumulation. Only UDP glucose pyrophosphorylase activity increased with increasing grain size. Detached rice panicles incubated in liquid medium containing 1% sucrose and 0.1% glutamine, in addition to minerals and vitamins, produced grains similar to those on intact plants. Sucrose level (0–1.5%) in the medium determined the extent of dry matter and starch accumulation and influenced physiological development of the ripening grains. Chemical and enzymic composition of the grain were similar to previously reported levels in grains of intact panicles analysed at regular intervals after anthesis. Addition of 3-P glycerate or K⁺ to the medium did not improve dry matter accumulation in the developing grain.     

Dynamic stiffness and crossbridge action in muscle

Small sinusoidal vibrations at 300 Hz were applied to frog sartorius muscle to measure the dynamic stiffness (Young's modulus) throughout the course of tetanus. For a peak-to-peak amplitude of 0.4% the dynamic Young's modulus increased from 1.5×10⁵ Nm^–2 in the resting state to 2×10⁷ Nm^–2 in tetanus. After correction for the external connective tissue, the dynamic Young's modulus of the muscle was almost directly proportional to the tension throughout the development of tetanus. The ratio of dynamic Young's modulus to tensile stress thus remained constant (with a value at 300 Hz of approximately 100), consistently with Huxley and Simmons' identification of the crossbridges as the source of both tension and stiffness.For a single crossbridge the ratio of stiffness to tension was 8.2×10⁷ m^–1 at 300 Hz; it is deduced from literature data that the limiting value at high frequencies is about 1.6×10⁸ m^–1. This ratio is interpreted on Harrington's (1971) model to show that crossbridge action can be explained by a helix-coil transition of about 80 out of the 260 residues in each S-2 myosin strand. It is also shown that a helix-coil model can account for the observed rapid relaxation of muscle without invoking any complex behaviour of the crossbridge head.     

Receptors for the complement C3d component and the Epstein-Barr virus are quantitatively coexpressed on a series of B-cell lines and their derived somatic cell hybrids

Various human Burkitt lymphoma and LCL lines established in vitro and their derived somatic cell hybrids were tested for their comparative EBV receptor levels in a virus binding assay. Their graded C3b and C3d complement receptor expression was estimated simultaneously by means of isotope labeled rosette marker cells. The receptor concentration of each cell line was related to Raji as the standard of comparison, K 562, P3HR-1, and YACUT were used as negative controls. In general, the charging curves for EBV and C3d receptors parallelled each other (r = 0.97) while C3b receptor charging showed no correlation (r < 0.60). In the Raji hybrids between the C3b receptor positive Raji parent and various patents that were negative for this receptor, C3b receptor expression was low or negative. In contrast, the C3d negative P3HR-1 line gave rise to hybrids, after fusion with receptor-positive cells, that were intermediate with regard to their C3d receptor expression. The host range restriction of the Epstein-Barr virus is determined at the receptor level. The close relationship between the EBV receptor and the C3d receptor, a B-lymphocyte-specific moiety, suggests that the moderate interaction with EBV with the B lymphocytes may have had a selective advantage, favoring the presence of EBV. Since EBV causes lytic infections after artificial introduction into nonnatural host cells, it may represent a B-lymphocyte-specific host range mutant, derived from an originally lytic herpesvirus with a much broader target cell range.     

Chromatographic resolution of amino acid adducts of aliphatic halides

Numerous xenobiotics are known to be bioactivated and to covalently bind to proteins, but the resulting amino acid adducts (AAAs) are unknown. In this study the AAAs of twelve ¹⁴C-labeled aliphatic halides were examined after formation in an in vitro microsomal system. After exhaustive solvent extraction of the precipitated microsomal protein, the AAAs were isolated by Pronase digestion, followed by filtration through a 500 mol. wt. exclusion membrane. The liberated AAAs were applied to a constant flow DC-4A cation exchange column, resolved by stepwise buffer elution, collected and counted for radioactivity. Column recovery for applied radioactivity was 100 ± 4%. Generally, 1–4 different AAAs (defined by eluting radioactivity) were resolved, with each organohalogen displaying a characteristic elution profile. Methyl iodide, trichloroethylene and 1,2-dichloroethylene had a single major AAA while bromotrichloromethane, 1,2-dibromoethane, 1,1,1-trichloroethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 2-bromo-2-chloro-1,1,1-trifluoroethane, chloroform and carbon tetrachloride had up to 4 AAAs or more, indicating combinations of binding site(s) and reactive intermediate(s). The single AAA formed following incubation of methyl iodide with the microsomes was identified as S-methylcysteine. Thus, this method appears capable of resolving binding sites and is the initial isolation step for identifying specific adducts to proteins.     

Kinetics of rapid RNA evolution in vitro

Summary A rapidly acquired partial resistance to the replicase antagonist, ethidium bromide (EB), seen by Spiegelman and coresearchers in Q RNA variants competitively replicating under defined conditions in vitro, reflected existence of a pool of mutant RNA molecules, preadapted to EB, and their cross-propagation from the pre-EB optimum species, MDV-1, and from other kindred variants, some of which remained undetected, according to this quantitative analysis of midivariant RNA replication kinetics. DNAlike features of their evolution, such as the cloning of variants from an MDV-1 subtype and a complicance with the fundamental theorem of natural selection, resulted from the suppression, both real and apparent, of intrinsic RNA heterogeneity through sampling and detection methods, and also by the ascendency of self-propagation over cross-propagation with advancement of a superior variant. The deficit in mean polymer fitness, compared with optimum levels, determines the lower limit of this heterogeneity. Stability conditions for frequency equilibrium and strategies for counteracting viral drug resistance have been considered.     

Cell Cycling of Astrocytes and Their Precursors in Primary Cultures: A Mevalonate Requirement Identified in Late G1, but Before the G1/S Transition, Involves Polypeptides

The relationship between mevalonate and cell cycling was investigated in developing glial cells. Primary cultures of newborn rat brains were serum-depleted (0.1%, vol/vol) for 48 h on days 4-6 in vitro, then returned to 10% calf serum (time 0). After 48 h, 70-80% of the cells were glial fibrillary acidic protein (GFAP)-negative by indirect immunofluorescence; 79 +/- 7% were GFAP-positive after an additional 3 days. Serum shift-up resulted in 12 h of quiescence, and then by 20 h (S phase) in increased proportions of cells synthesizing DNA (from 15 +/- 6% to 75 +/- 4% by bromodeoxyuridine immunofluorescence at 12 h and 20 h, respectively) and rates of DNA synthesis (42 +/- 6 versus 380 +/- 32 cpm/micrograms of protein/h of [3H]thymidine uptake). Additional mevalonate (25 mM) for 30 min at 10 h reversed the inhibition of DNA synthesis apparent with mevinolin (150 microM), an inhibitor of mevalonate synthesis, present from time 0. Cycloheximide added simultaneously with mevalonate prevented this reversal of inhibition. To cause arrest at G1/S, cultures were exposed to hydroxyurea between 10 and 22 h. By 3 h after hydroxyurea removal, bromodeoxyuridine-labeled nuclei increased from 0% to 75 +/- 9%, and DNA synthesis increased 10-fold. Mevinolin failed to inhibit these increases. Thus, primary astroglial precursors stimulated to progress through the cell cycle express a mevalonate requirement in late G1, but before the G1/S transition. The effect of mevalonate was characterized further as being brief (30 min) and as requiring polypeptides.     

Intraspecific variation in the response of rice (Oryza sativa) to increased CO2– photosynthetic, biomass and reproductive characteristics

Two rice ( Oryza sativa L.) cultivars of contrasting morphologies, IR-36 and Fujiyama-5, were exposed to ambient (360 μl l⁻¹) and ambient plus 300 μl l⁻¹ CO₂ from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO₂ resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO₂ environment. The photosynthetic response at 5% CO₂ and the response of CO₂ assimilation (A) to internal CO₂ (C_i) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO₂ were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO₂ environment with a significant increase in harvest index for IR-36 but not for Fujiyama-5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO₂ environment.     

Advances in cereal protoplast research

Beginning in 1986, plants have been regenerated from protoplasts of all of the important cereal species, including wheat, rice, maize, and barley, and grasses such as sugarcane. In addition, somatic hybrids/cybrids as well as transgenic plants with introduced useful agronomic traits have been obtained in several instances. This rapid and impressive progress in the genetic manipulation of cereals has been made possible by two critical technical advances during the past decade: the establishment of embryogenic suspension cultures as a source of totipotent protoplasts and the direct delivery of DNA into protoplasts for genetic transformation.