Nitrogen fixation in decaying chestnut logs

Summary Nitrogen fixation is shown to occur in decaying logs of American chestnut, Castanea dentata (Marsh.) Borkh., by acetylene reduction techniques, and its significance is considered in relation to log decomposition in forest ecosystems. re]19721109     

COMPARATIVE REPRODUCTIVE BIOLOGY OF ACER PENSYLVANICUM AND A. SPICATUM (ACERACEAE)

Pollination mechanisms and floral features affecting reproduction were examined in two closely-related species, Acer pensylvanicum and A. spicatum. Intra-specific crossing experiments, studies of pollen stainability and ovule number, and observations of the flowers in the field revealed that neither species bears functionally hermaphroditic flowers. Three flower-types were found in each species: staminate, pistillate, and a third type that is morphologically hermaphroditic. The latter form sheds viable pollen, but the pistil does not contain ovules. Pollen-ovule ratios of both species are in the range of expectation for a facultatively xenogamous reproductive system. Outcrossing is accomplished by entomophily in both species. A variety of insects from several orders visit the flowers; however bees in the genus Andrena (Hymenoptera: Andrenidae), especially A. milwaukeensis, are considered the most important pollinators of both maple species because of their fidelity to Acer, their intrafloral behavior, and their ability to carry pollen. However, flies are the most abundant visitors to A. pensylvanicum. Apomixis is an important means of reproduction in A. spicatum. Although floral phenology of these maple species overlaps within a geographical region they were never found blooming simultaneously when growing together.     

Steroidogenic electron transport in adrenal cortex mitochondria

Summary The flavoprotein NADPH-adrenodoxin reductase and the iron sulfur protein adrenodoxin function as a short electron transport chain which donates electrons one-at-a-time to adrenal cortex mitochondrial cytochromes P-450. The soluble adrenodoxin acts as a mobile one-electron shuttle, forming a complex first with NADPH-reduced adrenodoxin reductase from which it accepts an electron, then dissociating, and finally reassociating with and donating an electron to the membrane-bound cytochrome P-450 (Fig. 9). Dissociation and reassociation with flavoprotein then allows a second cycle of electron transfers. A complex set of factors govern the sequential protein-protein interactions which comprise this adrenodoxin shuttle mechanism; among these factors, reduction of the iron sulfur center by the flavin weakens the adrenodoxinadrenodoxin reductase interaction, thus promoting dissociation of this complex to yield free reduced adrenodoxin. Substrate (cholesterol) binding to cytochrome P-450_scc both promotes the binding of the free adrenodoxin to the cytochrome, and alters the oxidation-reduction potential of the heme so as to favor reduction by adrenodoxin. The cholesterol binding site on cytochrome P-450_scc appears to be in direct communication with the hydrophobic phospholipid milieu in which this substrate is dissolved. Specific effects of both phospholipid headgroups and fatty acyl side-chains regulate the interaction of cholesterol with its binding side. Cardiolipin is an extremely potent positive effector for cholesterol binding, and evidence supports the existence of a specific effector lipid binding site on cytochrome P.450_scc to which this phospho-lipid binds.     

Radioimmunoassay determinations of decreased amounts of α-L-fucosidase protein in fucosidosis

Purified human liver α-l-fucosidase (EC 3.2.1.51) has been radioiodinated by a chloramine-T procedure to a specific activity of 3.7·10⁶ dpm/μg protein without altering its apparent Michaelis constant for the 4-methylumbelliferyl substrate. This ¹²⁵I-labelled α-l-fucosidase has been used in development of a competitive binding radioimmunoassay for α-l-fucosidase which can detect 1–2 ng of enzyme protein and has been employed to quantify the amount of α-l-fucosidase protein in the liver and spleen from a patient with fucosidosis. Less than 1% of the normal amount of α-l-fucosidase protein is present suggesting that normal amounts of catalytically inactive α-l-fucosidase are not found in this disease.