Uptake of free amino acids by the diatom,Melosira mediocris

Individual ¹⁴C-labelled amino acids are rapidly removed from dilute solution in artificial sea water (0.2 mol 1^–1) by suspensions of Meliosira medocris. The rate of disappearance of radioactivity corresponds closely to removal of primary amines as determined by measurement of the rate of decrease of fluorescamine-positive material. Net removal of naturally occurring free amino acids from the sea water habitat from which the alga was isolated is demonstrated using high performance liquid chromatography. Removal of amino acids from natural sources makes a significant contribution to the carbon requirements of the alga as well as supplying significant amounts of amino nitrogen.     

Effect of Unilateral Decortication on Choline Acetyltransferase Activity in the Nucleus Basalis and Other Areas of the Rat Brain

Acetyl-coenzyme A: choline O-acetyltransferase (EC 2.3.1.6) (ChAT) enzyme activity was measured in the nucleus basalis and other microscopically identified brain areas at various times after unilateral cortical lesions were made in the rat. Initially, a significant decrease in ChAT activity was detected in the nucleus basalis ipsilateral to the lesion. However, after 120 days ChAT activity had apparently recovered, as levels of the enzyme at that time were not significantly different from control values. No changes in ChAT activity could be detected in any of the other brain areas similarly studied. The significance of these findings and their relationship to the morphological changes seen in neurones of the nucleus basalis after cortical lesions are discussed.     

Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes

Statistical methods for computing the standard errors of the branching points of an evolutionary tree are developed. These methods are for the unweighted pair-group method-determined (UPGMA) trees reconstructed from molecular data such as amino acid sequences, nucleotide sequences, restriction-sites data, and electrophoretic distances. They were applied to data for the human, chimpanzee, gorilla, orangutan, and gibbon species. Among the four different sets of data used, DNA sequences for an 895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979) gave the least reliable one. The DNA sequence data suggested that the chimpanzee is the closest and that the gorilla is the next closest to the human species. The orangutan and gibbon are more distantly related to man than is the gorilla. This topology of the tree is in agreement with that for the tree obtained from chromosomal studies and DNA-hybridization experiments. However, the difference between the branching point for the human and the chimpanzee species and that for the gorilla species and the human-chimpanzee group is not statistically significant. In addition to this analysis, various factors that affect the accuracy of an estimated tree are discussed.      

Pharmacological properties of canine intrapulmonary blood vessels

The contractile response of ring segments of large, medium, and small pulmonary arteries and veins of the dog to histamine, norepinephrine, and serotonin have been studied. The maximum contractile response to these drugs was normalized with respect to the maximal response obtained in stimulation with 127 mM K+. The small pulmonary artery was more reactive to histamine, norepinephrine, and serotonin when compared with large and medium pulmonary arteries. The medium and large pulmonary artery showed no difference in reactivity to histamine. However, the mean effective dose (ED50) values for these agonists among the different segments of pulmonary arteries showed no significant difference. The small and medium pulmonary veins demonstrated increased reactivity to histamine, but not norepinephrine and serotonin. The ED50 values also indicated that both small and medium veins were more sensitive to histamine when compared with the large pulmonary vein. The log concentration percent response curves for both small and medium pulmonary veins were displaced leftward (increased sensitivity) with respect to that for the large pulmonary vein. However, the reactivity and sensitivity to histamine between medium and small pulmonary veins were no different. The reactivity and sensitivity of different segments of pulmonary veins to norepinephrine and serotonin showed no significant differences among them. We conclude that histamine and other vasoactive substances, which are directly or indirectly related to mast cell degranulation, exert pharmacological effects on the pulmonary vasculature which possesses differential responsiveness at various levels of the vascular tree.     

Influences of medium consistency and shoot density on in vitro shoot proliferation of Populus alba × P. grandidentata

The in vitro shoot proliferation of Populus alba × P. grandidentata was affected by the medium consistency and shoot density, but not by three sizes of vessels. After 4 weeks of culture, the fresh weight and number of shoots per explant on liquid medium were significantly greater than those on agar-solidified medium. In particular, 3.2 shoots, 7 mm or longer per explant, were produced on liquid medium compared with 1.6 shoots per explant or agar-solidified medium. The fresh weight per explant after 4 weeks of culture on liquid medium and agar-solidified medium were 0.68 and 0.25 g, respectively. Increasing the number of shoots per vessel slowed the growth of the explants as measured by fresh weight and the number of shoots produced. There was little difference in the number of shoots produced between vessels with 1 or 2 shoots per vessel, but there were many fewer shoots produced when 3 shoots were placed in each vessel.Journal Paper No. J-11977 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 2210.     

Maximum shortening velocity of smooth muscle: zero load-clamp vs. afterloaded method

Previous reports from this laboratory of force-velocity relationships of canine tracheal smooth muscle (TSM) have presented maximum shortening velocities (Vmax) mathematically derived from the linearized transformation of the Hill equation (A. V. Hill, Proc. Roy. Soc. London, Ser. B., 126:136-195, 1938). Recent technical advances enable us to measure Vmax directly using an electromagnetic lever system that can instantaneously clamp to a zero load, thus we compared values of Vmax derived mathematically and those directly measured on the same TSM strips. Derived Vmax values from afterloaded isotonic shortening curves for loads greater than preload were 0.328 +/- 0.021 optimal length (lO)/s and were not significantly different from zero load-clamp measurements of 0.301 +/- 0.022 lO/s from the same (n = 15) muscles. These data indicate that Vmax values mathematically derived for TSM from conventional isotonic afterloaded force-velocity curves are valid estimates of zero load velocity, because they were not significantly different from values obtained by direct measurement using the zero load-clamp technique.     

Serological similarity of flagellar and mitotic microtubules

An antiserum to flagellar axonemes from sperm of Arbacia punctulata contains antibodies which react both with intact flagellar outer fibers and with purified tubulin from the outer fibers. Immunodiffusion tests indicate the presence of similar antigenic determinants on outer-fiber tubulins from sperm flagella of five species of sea urchins and a sand dollar, but not a starfish. The antibodies also react with extracts containing tubulins from different classes of microtubules, including central-pair fibers and both A- and B-subfibers from outer fibers of sperm flagella, an extract from unfertilized eggs, mitotic apparatuses from first cleavage embryos, and cilia from later embryos. Though most tubulins tested share similar antigenic determinants, some clear differences have been detected, even, in Pseudoboletia indiana, between the outer-fiber tubulins of sperm flagella and blastular cilia. Though tubulins are "actin-like" proteins, antitubulin serum does not react with actin from sea urchin lantern muscle. On the basis of these observations, we suggest that various echinoid microtubules are built of similar, but not identical, tubulins.     

High-yield trapping of EGF-induced receptor dimers by chemical cross-linking

The binding of epidermal growth factor (EGF) to its plasma membrane receptor results in the stimulation of a tyrosyl residue-specific protein kinase, which has been shown to be part of the receptor. The mechanism by which EGF binding give rise to the stimulation of kinase activity is not understood in detail; however, a number of recent studies have implicated receptor dimerization or oligomerization in this process. We prepared Triton X-100 extracts of A431 cells in which the concentration of EGF receptors was on the order of 10(-7) M. When samples of the extracts were incubated with or without EGF and then treated with the high-yield cross-linking reagent bis(sulfosuccinimidyl)suberate (BS3), covalent receptor dimers could be detected in high yield in samples that had been treated with both EGF and BS3, whereas only monomeric receptor was detected in untreated samples or in samples that had been treated with either EGF or BS3. The yield of receptor dimers trapped by cross-linking correlated with the stimulation of autophosphorylation by EGF and with the concentration of EGF present. EGF-induced receptor dimers were also efficiently cross-linked in highly purified receptor preparations, suggesting that EGF-induced dimerization is a process intrinsic to the receptor, requiring no additional accessory proteins.