KINETIC PROPERTIES OF CELLULOMONAS SP. PURINE NUCLEOSIDE PHOSPHORYLASE WITH TYPICAL AND NON-TYPICAL SUBSTRATES: IMPLICATIONS FOR THE REACTION MECHANISM

Phosphorolysis catalyzed by Cellulomonas sp. PNP with typical nucleoside substrate, inosine (Ino), and non-typical 7-methylguanosine (m⁷Guo), with either nucleoside or phosphate (P_i) as the varied substrate, kinetics of the reverse synthetic reaction with guanine (Gua) and ribose-1-phosphate (R1P) as the varied substrates, and product inhibition patterns of synthetic and phosphorolytic reaction pathways were studied by steady-state kinetic methods. It is concluded that, like for mammalian trimeric PNP, complex kinetic characteristics observed for Cellulomonas enzyme results from simultaneous occurrence of three phenomena. These are sequential but random, not ordered binding of substrates, tight binding of one substrate purine bases, leading to the circumstances that for such substrates (products) rapid-equilibrium assumptions do not hold, and a dual role of P_i, a substrate, and also a reaction modifier that helps to release a tightly bound purine base.     

Offspring of older parents are smaller—but no less bilaterally symmetrical—than offspring of younger parents in the aquatic plant Lemna turionifera

Offspring quality decreases with parental age in many taxa, with offspring of older parents exhibiting reduced life span, reproductive capacity, and fitness, compared to offspring of younger parents. These “parental age effects,” whose consequences arise in the next generation, can be considered as manifestations of parental senescence, in addition to the more familiar age‐related declines in parent‐generation survival and reproduction. Parental age effects are important because they may have feedback effects on the evolution of demographic trajectories and longevity. In addition to altering the timing of offspring life‐history milestones, parental age effects can also have a negative impact on offspring size, with offspring of older parents being smaller than offspring of younger parents. Here, we consider the effects of advancing parental age on a different aspect of offspring morphology, body symmetry. In this study, we followed all 403 offspring of 30 parents of a bilaterally symmetrical, clonally reproducing aquatic plant species, Lemna turionifera, to test the hypothesis that successive offspring become less symmetrical as their parent ages, using the “Continuous Symmetry Measure” as an index. Although successive offspring of aging parents older than one week became smaller and smaller, we found scant evidence for any reduction in bilateral symmetry.     

The Asymmetry of (−)α‐Pinene as Revealed from its Raman Optical Activity Spectrum

An algorithm is employed to retrieve the differential bond polarizabilities of the C‐C bonds from the Raman optical activity (ROA) spectrum of (?)α‐pinene. (?)α‐pinene possesses two asymmetric centers (carbon atoms) and a local mirror symmetry. These differential bond polarizabilities show the characteristics of the asymmetry around the asymmetric carbons with respect to the mirror reflection. This analysis is accompanied along with the ROA mode signatures and the calculated β(G ')² and β(A)²which show the ROA coupling mechanisms involving the electric/magnetic dipoles and the electric dipole/quadrupole, respectively. Chirality 25:600–605, 2013. © 2013 Wiley Periodicals, Inc.     

Wernicke's area homologue in chimpanzees (Pan troglodytes) and its relation to the appearance of modern human language

Human language is distinctive compared with the communication systems of other species. Yet, several questions concerning its emergence and evolution remain unresolved. As a means of evaluating the neuroanatomical changes relevant to language that accompanied divergence from the last common ancestor of chimpanzees, bonobos and humans, we defined the cytoarchitectonic boundaries of area Tpt, a component of Wernicke''s area, in 12 common chimpanzee brains and used design-based stereologic methods to estimate regional volumes, total neuron number and neuron density. In addition, we created a probabilistic map of the location of area Tpt in a template chimpanzee brain coordinate space. Our results show that chimpanzees display significant population-level leftward asymmetry of area Tpt in terms of neuron number, with volume asymmetry approaching significance. Furthermore, asymmetry in the number of neurons in area Tpt was positively correlated with asymmetry of neuron numbers in Brodmann''s area 45, a component of Broca''s frontal language region. Our findings support the conclusion that leftward asymmetry of Wernicke''s area originated prior to the appearance of modern human language and before our divergence from the last common ancestor. Moreover, this study provides the first evidence of covariance between asymmetry of anterior and posterior cortical regions that in humans are important to language and other higher order cognitive functions.     

A study on the topological distribution of phospholipids in microsomal membranes of chick brain using phospholipase C and trinitrobenzenesulfonic acid

The transbilayer distribution of phospholipids in chicken brain microsomal membranes has been investigated using trinitrobenzenesulfonic acid and phospholipase C from Clostridium weichii. The exposure of intact microsomes to trinitrobenzenesulfonic acid showed that the labelling of aminophospholipids followed biphasic kinetics, indicating that these membranes contain a fast- and a slow-reacting pool of aminophospholipids. Use of microsomes radioiodinated on their surface led to the conclusion that the fast-reacting pool may be located on the outer leaflet of the microsomal vesicles. It contains about 35% of the phosphatidylethanolamine, 29% of the ethanolamine plasmalogens and 18% of the phosphatidylserine. The treatment of intact microsomes with the phospholipase C Cl. welchii produced the hydrolysis of 50% of the phospholipids without any loss of their permeability properties, indicating that they are not permeable to the hydrolase. Phospholipids extracted from the microsomes were hydrolyzed rapidly by the phospholipase C with the exception of phosphatidylserine and phosphatidylinositol. In intact microsomes about 90% of phosphatidylcholine, 32% of ethanolamine phospholipids and 60% of sphingomyelin were accessible to the phospholipase. These results suggest that the phospholipids have an asymmetric distribution in chicken brain microsomes, the external leaflet containing about 75% of the choline phospholipids and 25% of the aminophospholipids, whereas an opposite distribution is observed in the inner leaflet.     

Purine metabolism in the bloodstream forms of trypanosoma gambiense and Trypanosoma rhodesiense

Bloodstream forms of Trypanosoma brucie gambiense and Trypanosoma brucei rhodesiense are incapable of de novo purine synthesis. Purine bases are converted directly to ribonucleotides and with the exception of guanine, are stable. Guanine is incorporated directly into ribonucleotides and also deaminated to xanthine. Purine ribonucleosides are hydrolyzed rapidly; these reactions may limit their incorporation since purine bases label the nucleotide pools more efficiently than do ribonucleosides. The apparent order of salvage efficiency for ribonucleosides is adenosine>inosine>guanosine>xanthosine for both organisms. T. b. gambiense salvages purine bases in the same order, while T. b. rhodesiense salvages purine bases in the order hypoxanthine>adenine>guanine>xanthine.     

Effect of Probe Size on the Concentration of Brain Extracellular Uric Acid Monitored with Carbon Paste Electrodes

Abstract: We have investigated further the anomalously high concentration of brain extracellular uric acid detected with in vivo sampling probes reported recently. The contribution by uric acid and 5-hydroxyindoleacetic acid (5-HIAA) to peak 2 recorded in rat striatum with chronically implanted carbon paste electrodes (CPEs) of different sizes was estimated by comparing peak current densities and the effect of the monoamine oxidase inhibitor pargyline. The concentration of uric acid in the extracellular fluid was some 50 times greater for 320-μm-diameter CPEs than for 160-μm-diameter electrodes, where the urate level was estimated at ∼1 μ M. The concentration of 5-HIAA was similar for 320-, 260-, and 160-μm-diameter CPEs. These data provide an explanation for the previously observed differences in 5-HIAA/urate ratios re corded with 320-μm-diameter CPEs and smaller carbon fibre electrodes. The results also indicate that chronically implanted sampling probes of diameter >160 μm perturb the surrounding tissue, which produces uric acid by a mechanism yet unknown, although preliminary histological data suggest that glial cells may be involved.     

Localization of 2′,3′-cyclic nucleotide 3′-phosphodiesterase in human erythrocyte membranes

The location of 2′,3′-cyclic nucleotide 3′-phosphodiesterase in human erythrocyte membranes was determined. This was accomplished by comparing the enzyme's accessibility with that of glyceraldehyde-3-phosphate dehydrogenase (cytoplasmic surface marker) and acetylcholinesterase (external marker) in sealed and unsealed ghosts and normal and inverted membrane vesicles. The results showed that 2′,3′-cyclic nucleotide 3′-phosphodiesterase, like glyceraldehyde-3-phosphate dehydrogenase, meets several criteria for an inner (cytoplasmic) membrane location: (1) the enzyme was accessible to substrate in unsealed ghosts and inside-out vesicles but not in sealed or right-side-out vesicles, (2) latent activity in sealed ghosts could be exposed with detergent (Triton X-100), (3) activity in unsealed ghosts was gradually sequestered during resealing and could be re-exposed with detergent, and (4) the enzyme was susceptible to trypsin proteolysis only in unsealed ghosts. These results demonstrate that the active site of 2′,3′-cyclic nucleotide 3′-phosphodiesterase faces the cytoplasm of erythrocytes and that the enzyme may not span the lipid bilayer of the membrane. The localization of the phosphodiesterase on the inner membrane surface of erythrocytes suggests that the similar enzyme of myelin may be embedded within the major dense line of the compact lamellae.