Folate in demethylation: The crystal structure of the rat dimethylglycine dehydrogenase complexed with tetrahydrofolate

Dimethylglycine dehydrogenase (DMGDH) is a mammalian mitochondrial enzyme which plays an important role in the utilization of methyl groups derived from choline. DMGDH is a flavin containing enzyme which catalyzes the oxidative demethylation of dimethylglycine in vitro with the formation of sarcosine (N-methylglycine), hydrogen peroxide and formaldehyde. DMGDH binds tetrahydrofolate (THF) in vivo, which serves as an acceptor of formaldehyde and in the cell the product of the reaction is 5,10-methylenetetrahydrofolate instead of formaldehyde. To gain insight into the mechanism of the reaction we solved the crystal structures of the recombinant mature and precursor forms of rat DMGDH and DMGDH–THF complexes. Both forms of DMGDH reveal similar kinetic parameters and have the same tertiary structure fold with two domains formed by N- and C-terminal halves of the protein. The active center is located in the N-terminal domain while the THF binding site is located in the C-terminal domain about 40 Å from the isoalloxazine ring of FAD. The folate binding site is connected with the enzyme active center via an intramolecular channel. This suggests the possible transfer of the intermediate imine of dimethylglycine from the active center to the bound THF where they could react producing a 5,10-methylenetetrahydrofolate. Based on the homology of the rat and human DMGDH the structural basis for the mechanism of inactivation of the human DMGDH by naturally occurring His109Arg mutation is proposed.     

Interhemisphere asymmetry and the constancy of visual perception of large and small sizes

The constancy of perception of linear 3–40-cm sizes at a distance of 0.7 to 5.6 m was studied. The results of investigations carried out on 66 subjects are presented. Sizes less than 10 cm and more than 10 cm are perceived according to different laws. Large sizes, as they are moved away, are assessed according to two modes of perception: aconstantly (with a diminution of the size value) and constantly (with the preservation of the apparent size value). The sizes not exceeding 10 cm are reassessed with an increase in the distance to the extent that reevaluation of the small size value attains 40%. It is evident that only one modus of perception— hyperconstancy—exists for sizes less than 10 cm.     

Compartmentation of Assimilate Fluxes in Leaves

Abstract: Sugar levels in the apoplast of assimilate exporting leaves were studied in two groups of plant species with contrasting structures of companion cells in minor veins. These species are termed either "symplastic" (with intermediary cells) or "apoplastic" (with transfer or ordinary cells). Sugars were measured in intercellular washing fluid after extracting the apoplast by an infiltration-centrifugation technique. During the course of a day, sugar contents in the apoplast were, in general, lower in species with intermediary cells than in species with transfer or ordinary cells. In "symplastic" species, apoplastic sucrose concentrations were between 0.3 and 1 mM. In "apoplastic" species with transfer cells, they ranged between 2 and 6 mM. Apoplastic hexose contents were between 0.3 and 1 mM irrespective of presumed transport mode. "Symplastic" and "apoplastic" plants differed markedly in their response to a'translocation block. In "symplastic" plants, inhibition of assimilate export left apoplastic concentrations of sucrose and hexoses unchanged, whereas in "apoplastic" plants sugar levels increased, the maximal increase being observed with sucrose. In these plants, concentrations of sucrose were two to six times higher in the apoplast under export inhibition than in control leaves. The data suggest a different role of the leaf apoplast in the compartmentation and export of assimilates in the two plant groups under study.     

Contribution of a photoreactivable component to the oxygen effect observed in certain rad mutants of Saccharomyces cerevisiae after exposure to high energy electrons

It is shown that a fraction of damage induced by high energy electrons (25 MeV) in certain rad mutants of the yeast Saccharomyces cerevisiae can be photoreactivated. The photoreactivable damage contributes to the lethal effect of this type of irradiation and modifies the oxygen effect. Using photoreactivating light or nigrosin, the amount of photoreactivable damage is reduced and the oxygen enhancement ratio (OER) for yeast mutants increases approximately to the OER found in wild-type cells.     

The effect of cytostatics and corticosteroids on the phagocytic and fungicidal activity of the neutrophilic granulocytes

In vitro tests have revealed that cytostatic agents and corticosteroids, introduced in vivo, produce an inhibitory effect on the phagocytic activity of mouse neutrophil granulocytes and on their capacity for the destruction of Candida albicans blastospores. The action of the above-mentioned preparations may be an important pathogenetic factor which when introduced into the animals, contributes to the development of candidiasis.     

Effect of local use of carbostimulin on the activity of energy metabolism enzymes in mandibular alveolar process tissue in the rat

The local carbostimulin effect on the oral cavity tissue under spontaneous parodontosis of albino rats stimulates the energy and biosynthetic process. A significant decrease in atrophy of the alveolar process confirms a positive effect of carbostimulin on the jaw bone tissue.     

NADH diaphorase polymorphism in goat erythrocytes

This paper describes for the first time polymorphism of the erythrocyte diaphorase in goats. Three diaphorase 1 phenotypes were observed in the red cells of goats. Breeding data indicated that polymorphism was controlled by two autosomal codominant alleles, DiaF and DiaS, the frequencies of which were determined in 14 different Spanish breeds of goat.     

Diencephalic afferents of the rat hippocampus

Connection between diencephalic structures and the hippocampus were investigated in albino rats by the retrograde horseradish peroxidase axon transport method in albino rats. After injection of horseradish peroxidase into the dorsocaudal zone of hippocampal area CA₁, cells labeled with the enzyme were found in nuclei of the thalamus and hypothalamus. The sources of hippocampal afferents were found to be both nonspecific (n. reuniens, n. centralis lateralis, n. centralis medialis) and specific (n. anterodorsalis, n. anteroventralis, n. lateralis anterior, n. lateralis) thalamic nuclei. Axons to the hippocampus also are sent by neurons of n. paraventricularis and n. perifornicalis of the hypothalamus. The results are evidence that direct pathways from structures with sensory inputs run to the hippocampus from the thalamus.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 359–364, July–August, 1981.