Fluorine nuclear magnetic resonance spectra of rabbit carbonmonoxyhemoglobin

Carbonmonoxyhemoglobin prepared from protein isolated from rabbits maintained on a diet supplemented with 4-fluorophenylalanine (Phe (4F)) has been studied by fluorine NMR spectroscopy. Substitution of Phe(4F) appears to take place randomly at the sixteen nonequivalent phenylalanine positions of the globins; examination of hybrid hemoglobins in which only one type of globin chain contained the fluorinated amino acid, as well as changes in the spectrum upon exposure to oxygen, aided in the assignment of fluorine resonances from the alpha- or beta-globin chains. The effects of modification of Cys-beta-93 with a spin label and variation of pH and sample temperature on the spectrum were also examined. These data in association with theoretical estimates of aromatic ring current and van der Waals effects on chemical shifts were used to support tentative assignments of several signals observed to specific amino acid residues. Evidence suggesting the presence of two conformational forms of the protein, possibly due to disorder of the heme groups, is described.     

ENVIRONMENTAL INFLUENCES ON NECTAR PRODUCTION IN MILKWEEDS (ASCLEPIAS SYRIACA AND A. EXALTATA)

Cross-comparisons of nectar production data are complicated because different workers use bags made of various materials to exclude animal visitors. Using clonal populations of Asclepias syriaca and A. exaltata in northern Virginia, we carefully measured the effects of four bagging treatments (bridal veil, pellon, paper, plastic) on microenvironment (temperature, relative humidity) and nectar production (volume, concentration, sucrose amount) over the course of a day. In general, bridal veil bags changed the microenvironment least relative to unbagged controls. Plastic bags resulted in higher temperatures and constantly higher relative humidities. Temperature and relative humidity were also elevated, though less dramatically, in paper and pellon bags. Under more humid conditions, flowers contained larger volumes of more dilute nectar. Therefore, researchers who wish to obtain nectar production data that reflect natural field conditions should use bridal veil, or a material with similar properties, to bag inflorescences. We also performed a watering experiment, involving the addition of the equivalent of a 10-cm rain to the A. syriaca plot. After watering, nectar volumes and sucrose amounts were increased approximately twofold.     

Improved methods of estimating root length using a photocopier,a light box and a bar code reader

Photocopying was found to be a rapid method of making a permanent record of a root sample. The method used produced a copy with white roots against a black background. Manual estimates of root length were made from photocopies using a light box. The number of intersections visible when laid over a copy of a white on black regular square grid was counted. Automated estimates of root length were made by scanning a photocopy with a bar code reader in place of a pen in a computer-driven graph plotter. Roots >0.2 mm diameter were resolved with precision and speed.     

The differential protection by WR2721 of skin versus growing cartilage following irradiation in weanling rats

The potential for radioprotection of growing cartilage by the thiophosphate WR2721 was evaluated in weanling rats using single fractions of irradiation. Protection of acute skin toxicity was monitored simultaneously. Single doses of 600, 1200, 1800, or 2400 cGy were administered to the left tibia of CrL:CD(SD)BR female rats in groups of 12. Identically treated groups were injected with 310 mg/kg WR2721 (2/3 the determined LD50/30) in a concentration of 26 mg/ml intraperitoneally 15 min prior to irradiation. Rats untreated or given WR2721 without radiation served as control groups. Radiographs of the irradiated and unirradiated tibiae for each animal were obtained weekly to the date of sacrifice at 80 days following the initial treatment. Skin toxicity was assessed weekly starting on the second week using Moulder's scale (J.E. Moulder, J.J. Fischer, and A. Casey, Radiology 115, 465-470 (1975]. No significant difference in bone growth as measured by tibial lengths for the WR2721-treated or untreated animals was observed. Skin toxicity including moist desquamation occurred in irradiated limbs and was substantially less in rats treated with WR2721. As opposed to previous work with cysteamine, WR2721 as administered had no significant radioprotective effect on tibial growth in weanling rats but substantially reduced the accompanying skin toxicity.     

Protein metabolism in the mouse during pregnancy and lactation.

Protein synthesis was measured in vivo in the whole body and in a number of individual tissues in mice at various stages of pregnancy and lactation. The absolute rate of protein synthesis in the whole body increased from 640 mg/day in virgin mice to 1590 mg/day by day 18 of pregnancy, and to 2100 mg/day by day 15 of lactation. Large proportions of these increments were contributed by the rapidly growing foetuses and placentae in the pregnant animals and by protein synthesis in the mammary glands during lactation. In addition, a substantial stimulation of growth and protein synthesis was also observed in the liver and the gastrointestinal tract. Gastrocnemius muscle showed no changes in protein metabolism, indicating that in the well-fed mouse this tissue is not required to play a role as a protein reserve during pregnancy and lactation.