Use of anin situ labeling technique for the determination of seasonal14C distribution in Ponderosa pine

A¹⁴C labeling apparatus was developed to permit the labeling of four-year-old Ponderosa pine with¹⁴CO₂ in the field. The labeling system is a completely closed canopy system with¹⁴CO₂ monitored by a GM tube ratemeter apparatus. The level of¹⁴CO₂ corresponding to ambient levels is monitored by a microloggercomputer which controls a¹⁴CO₂ generating system. The generated¹⁴CO₂ is mixed in the canopy by circulating the atmosphere with 12V diaphram pumps. The portable system requires little operator attention. At approximately monthly intervals over a one-year period two four-year-old Ponderosa pine trees were labeled for three to five days using this labeling apparatus. After an assimilate distribution period, one tree was excavated and analyzed for¹⁴C distribution. During late spring and early summer most of the carbon assimilated (>60%) was found in the active growing tips and new needles, with little being allocated to the roots (<10%) or woody material (<20%). During mid to late fall there was an increase in root labeling along with an increase in carbon going to woody material. Over the winter period, most of the fixed carbon (65%) resided in the older leaves. The early spring labeling period showed another pulse of root labeling along with some labeling of woody tissues.     

Influence of phosphatidylcholine/cholesterol molar ratios in liposomes on cholesterol reactivity with cholesterol:oxygen oxidoreductase]

The reactivity of sonicated phosphatidylcholine-cholesterol liposomes with cholesterol : oxygene oxydoreductase, an enzyme which catalyses the oxidation of the 3 beta hydroxyl group of cholesterol to a ketone group, is compared with that of ternary system phosphatidylcholine-cholesterol-Thesit. Regardless to the phosphatidylcholines nature and the phosphatidylcholine/cholesterol molar ratio (R), the enzymatic oxidation rate of liposomal cholesterol is slower than when the reaction is developed in the present of Thesit, a surfactif agent which destroyes the lamellar particles. This is true whether Thesit is added during preparation of dispersions or during incubation with cholesterol oxydase. The enzymatic oxydation rate of cholesterol of ternary systems phosphatidylcholine-cholesterol-Thesit is independent of the (R) value and the phosphatidylcholine fatty acid unsaturation, whereas that of phosphatidylcholine-cholesterol dispersions depends on these two parameters. The reaction rate increases in the order: dipalmitoylphosphatidylcholine to yolk egg phosphatidylcholines, and dioleylphosphatidylcholine. The optimal conditions for cholesterol oxidation were found to be R = 0.5. This result is not affected by the phosphatidylcholines nature. In order to explain these data, various hypotheses are considered. In particular, the weak liposomal cholesterol reactivity with cholesterol oxidase could result from an inhibitory effect on the enzyme-substrate combination due to the polar phosphorylcholine groups.     

Comparison of the acid denaturation of several hemoglobins which differ in amino acid sequence

There are pronounced differences in kinetic and thermodynamic stability between human and horse hemoglobins. Since the amino acid sequences of the α, β dimers of horse and human hemoglobins differ in 61 locations, it is difficult to account for them in terms of specific direct or indirect effects of the sequence differences. Rhesus hemoglobin differs from human in only 12 locations and its stability resembles that of human more closely than does horse, although pronounced differences remain. The stabilities of rhesus ferrihemoglobin and deoxyhemoglobin (Hb⁺ and Hb °) are intermediate between those of the corresponding high-spin forms of horse and human hemoglobin; but there are only small or negligible differences between the low-spin forms (carbonylhemoglobin and oxyhemoglobin) of the two species. The equilibrium isotherm between native and acid unfolded forms of rhesus Hb⁺ resembles that of horse more than that of human, but it is slightly more stable and slightly less cooperative. The effects of octanol on the rates of unfolding of rhesus ferrihemoglobin are only slightly smaller than with human. There is no effect of octanol on the unfolding rate of any of the CO hemoglobins. Unlike the equilibria of horse and human, octanol is also without effect on the unfolding equilibrium of rhesus ferrihemoglobin, and thus qualifies as a true catalyst of the initial stage of the acid unfolding reaction of the monkey ferriprotein. Differences in stability are tentatively attributed to a limited number of the 12 differences between the two proteins.     

Characterization and physico-chemical properties of human transcortin]

The molecular weight of human transcortin, calculated from the sedimentation coefficient, was found to be 49,500, thus slightly lower than previously reported values. After purification, human transcortin trended to polymerize rapidly, with participation of both non covalent bonds and one disulfide bridge per dimer. The physicochemical parameters, the amino-acid and carbohydrate composition were determined; its stability was studied under different conditions. Preliminary structural studies showed that the N-terminal sequence of the polypeptide chain was: Met-Asp-Pro-Asn-Ala-Ala-Tyr-Val and that the C-terminal amino acid was leucine.     

Changes in amino acid transport in the rat pancreas in response to fasting and feeding

Transport of amino acids (in vitro) in the rat pancreas is affected by the nutritional state of the animal. A fast of 24 h (young animals) or 48 h (adult animals) reduces the rate of amino acid uptake in the isolated rat pancreas in vitro. In contrast, refeeding of animals after a fast shows an increase in transport in young as well as adult animals.The effects of refeeding after a fast are mimicked to a significant extent by injection of mixtures of pancreozymin and carbamylcholine. Addition of these agents in vitro has no effect.The incorporation of amino acids into the total proteins of the rat pancreas follows the pattern of amino acid uptake. Even at high external levels of glycine (5 mM), incorporation increases although the glycine level in the cell is in excess of 25 mM. Reduction of glycine uptake by ouabain by 75% results in a substantial (44%) diminution of amino acid incorporation into proteins. The data suggest that inhibition of amino acid incorporation under the various metabolic conditions examined is due largely to a decreased availability of amino acids.     

The effect of sodium chlorate and nitrapyrin on the nitrification mediated nitrosation process in soils

Summary The influence of total nitrification to nitrate or partial nitrification to nitrite on the soil organic nitrogen status was examined. NH ₄ ⁺ –¹⁵N was added to the soil in the absence and the presence of NaClO₃, respectively nitrapyrin. The first chemical inhibits only nitrate formation, the second inhibits total nitrification. The accumulation of nitrite nitrogen in the soil at levels up to 5 mg kg^–1 increased the loss of nitrogen. Yet, it did not increase the binding of mineral nitrogen into soil organic matter, relative to the control soil. The data suggest that the biochemistry of the nitrite formation process, rather than the levels of nitrite ions formed, are of primary importance in the role of nitrification mediated nitrosation of soil organic matter.     

Ataxia telangiectasia: the effects of chemical mutagens and x-rays on sister chromatid exchanges in blood lymphocytes

It is now possible to examine in detail exchanges between sister chromatids (SCEs) and to attempt to investigate the relationships of such exchanges to aberration formation and DNA-repair mechanisms. The frequency of SCEs is dramatically increased by chemical mutagens and may reflect the level of DNA damage. Lymphocytes from patients with ataxia telangiectasis (AT) show high levels of spontaneous chromosome damage and are hypersentive to ionising radiations and it was of interest to examine the levels of SCE induced in these cells by various mutagens. The frequencies of SCE after treatment with X=rays or three chemical mutagens were equivalent to those in normal cells. The effects of fluorodeoxyuridine and deoxycytidine on SCE frequencies were also tested.