Micrococcus luteus endonucleases for apurinic/apyrimidinic sites in deoxyribonucleic acid. 2. Further studies on the substrate specificity and mechanism of action

Two endonucleases specific for DNA-containing apurinic or apyrimidinic sites (AP-endonucleases A and B) have been isolated from Micrococcus luteus and highly purified. These enzymes have no exonuclease activity. Both AP-endonucleases hydrolyze DNA-containing apurinic or apyrimidinic sites at the 5' end of the lesion, thus generating 3'-hydroxyl and 5'-phosphoryl end groups. DNA-containing pyrimidine dimers, introduced at low doses of UV, are not hydrolyzed, whereas DNA-containing lesions, introduced at high doses of UV or by gamma irradiation are nicked by either AP-endonuclease. During hydrolysis of apurinic DNA, neither of the AP-endonucleases acts as a processive enzyme.     

Effect of aging on the morphology and function of the thyroid gland of the cream hamster

Summary The effect of aging on the morphology and function of the thyroid gland of the cream hamster was studied by light and electron microscopy coupled with autoradiography or histochemistry.Morphologically, aging induces an accumulation of lysosomal dense bodies and a loss of the phagocytosis of colloid droplets after stimulation with TSH. Iodine uptake and organification occur normally and thyroglobulin synthesis, estimated by autoradiography with ³H-leucine, is not different from that observed in young animals. The basal T₄ and T₃ plasma levels are lower in the old animals. A low iodine diet administered for several months prevents the age related accumulation of lysosomal dense bodies. Hormone secretion seems to proceed by two different mechanisms; phagocytosis of colloid droplets, the classical mechanism that decreases with age, and an additional mechanism, probably micropinocytosis, that is maintained during the whole lifespan.Presented at the First French Congress of Endocrinology, Montpellier, September 1980Work was performed under contracts n 3.4523.79 and n 3.4512.80 of the Fonds de la Recherche Scientifique Médicale, thanks to a grant of the Ministère Belge de la Politique Scientifique (Action concertée) and with the help of the Fondation Interuniversitaire pour la Recherche du Processus du Vieillissement, Belgium     

The Ostrich (Struthio camelus) egg-white lysozyme

Summary The purification of Ostrich (Struthio camelus) egg-white lysozyme is reported. The quantitative amino acid composition, the molecular weight, the N-terminal sequence (34 amino acids) as well as kinetic studies allow to range this enzyme among the goose type lysozymes.106th communication on lysozymes.     

Electron microscopic study of the mandibular glands of Kalotermes flavicollis Fabr. (Isoptera; Calotermitidae)

Summary The mandibular glands of Kalotermes were examined in different castes. They showed sexual dimorphism in the soldiers and primary reproductives. Moreover, in female soldiers and queens, mandibular gland cells contained numerous crystalline structures of mitochondrial origin. The role of these glands (secretion of saliva or pheromone) is discussed.

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Résumé Les glandes mandibulaires de Calotermes sont étudiées dans les différentes castes. Elles présentent un dimorphisme sexuel chez les soldats et les sexués. Après la mue imaginale, les cellules glandulaires ont toujours une activité sécrétrice. De plus, chez les soldats femelles et les reines, elles contiennent de nombreuses formations cristallines d'origine mitochondriale. Le rôle de ces glandes (sécrétion de salive ou de phéromone) est discuté.

     

Replication of prophage P1 during the cell cycle of Escherichia coli.

Summary We have followed, by DNA-DNA hybridization, the variation in the number of copies of prophage P1 relative to two chromosomal markers when the doubling time of the host cells is modified by a change in carbon source. The ratio of P1/chromosome terminus undergoes a twofold decrease when the cell doubling time increases from 24 to 215 min, whereas the ratio of P1/chromosome origin increases 1.4 fold; both ratios tend towards unity at slow growth rates. This suggests that the replication of prophage P1 is not simultaneous with chromosome initiation or chromosome termination. The chromosome replication time is unaffected by the presence of P1, and remains constant over the range of doubling times studied, with a value of about 40 min. Following amino acid starvation, the P1/chromosome origin ratio increases from 0.7 to 0.9, suggesting that P1 retains the ability to replicate after chromosome initiation has stopped and in the absence of essential amino acids. The results are discussed with reference to similar studies done on F and R1.     

Non-Linear Patterns of Complex Ramification Schemes in Higher Plants (Proposition for an Insight)

Die Seitenzweige von Cupressus sempervirens L. sind auf vier Orthostichen in scheinbar mehr oder weniger zufälligen, voneinander unabhängigen Mustern angeordnet. Eine auf L-Systeme sich berufende mathematische Konstruktion gestattet die Definition eines Morphismus. Acht Parameter, Periodizität der absoluten Wachstumsrate der zugrundeliegenden theoretischen Serien, die Väriation dieser Raten in komplementaren Unterserien und eine Schwellenreaktion sind die Hauptargumente.     

Application of the imidate procedure to α-d-galactosyltion

Using the imidate procedure, 2,3,4,6-tetra-O-benzyl-1-O-(N-methylacetimidoyl)-β-d-galactopyranose was condensed with various monosaccharides to provide, in good yield and with high stereoselectivity, α-linked disaccharides.