Purine salvage as metabolite and energy saving mechanism in Camelus dromedarius: the recovery of guanine

The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu.     

Purification of smooth-muscle myosin free of calmodulin and myosin light-chain kinase. Susceptibility to oxidation.

Smooth-muscle myosin purified as described by Persechini & Hartshorne [(1983) Biochemistry 22, 470-476] contains trace amounts of calmodulin and myosin light-chain kinase, which can be removed by Ca2+-dependent hydrophobic-interaction chromatography followed by calmodulin-Sepharose affinity chromatography. The resultant column-purified myosin exhibits properties similar to those of the non-purified myosin, e.g. actin activation of the Mg2+-ATPase requires Ca2+/calmodulin-dependent phosphorylation of the two 20 kDa light chains. However, unlike the non-purified myosin, the column-purified myosin undergoes a time-dependent transition to a form which no longer requires phosphorylation for actin activation of the myosin Mg2+-ATPase. This transition is identified as a time-dependent change in conformation of the column-purified myosin from a 10 S to 6 S form and is caused by slow oxidation of the column-purified myosin, since it could be prevented by storage under N2 and reversed by 5 mM-dithiothreitol.     

Fluorescence technique for comparative studies of substrate-binding subsites in serine proteinases. Application to subtilisins.

A fluorescence technique for comparative studies of substrate-binding subsites in serine proteinases is described. It consists of: selective labelling of the corresponding subsites with a fluorescent group by using N alpha-dansyl(5-dimethylaminonaphthalene-1-sulphonyl)ated peptide chloromethanes containing different numbers of amino acid residues, and probing the immediate environment of the subsites by quenching experiments using ionic and neutral quenchers. Intramolecular distances between the subsites and particular chromophores can be also determined. The technique is of general applicability to all serine proteinases. The above mentioned approach was applied to two proteinases: subtilisin Novo and mesentericopeptidase. It was concluded that the substrate-binding site of mesentericopeptidase is considerably more polar than that of subtilisin Novo. Intramolecular distances between the labelled subsites and tryptophan residues in the two proteinases were determined.     

Nutrient conservation strategies in native Andean‐Patagonian forests

Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests.     

Dissociation of inductive from differentiative signals transmitted by C8-substituted guanine ribonucleosides to B cells from SJL mice

A hitherto unknown defect in the immune responsiveness of B lymphocytes from SJL mice has enabled us to distinguish two qualitatively distinct classes of signal delivered to B cells by C8-substituted guanine ribonucleosides. This defect renders B cells from SJL mice unresponsive to the inductive (early acting) signal of 8-mercaptoguanosine (8MGuo) that culminates in mitogenesis and nonspecific secretion of immunoglobulin. Unresponsiveness is not attributable to a shift in either the dose-response or kinetic profiles, nor can the presence of suppressor cells be demonstrated. In striking contrast, however, SJL B cells exhibit normal responsiveness to the differentiative (T cell-like, or late acting) signal provided by the substituted nucleoside. This signal enables SJL B cells, depleted of T cells, to respond to T cell-dependent antigens, and synergizes with T cell-derived lymphokines. These data suggest 1) that nonspecific secretion of immunoglobulin is dependent on both inductive and differentiative signals, 2) that antigen alone can supply an effective inductive signal for antigen-specific responses, and 3) that the SJL mouse will provide a useful model for selective study of inductive vs differentiative events.     

Anti-My-26: a monoclonal antibody inhibiting human phagocyte chemiluminescence

Anti-My-26, a mouse monoclonal IgG1 antibody, was raised against human granulocytes and has been shown to inhibit luminol-enhanced, glucose-independent chemiluminescence (CL) of human granulocytes (or monocytes) responding to the soluble secretagogues A23187 or ionomycin (calcium ionophores) and phorbol myristate acetate (PMA). Anti-My-26 inhibition of CL was reversible and was dependent on both secretatogue and monoclonal antibody concentration. This inhibition appeared to be directed at the component of granulocyte CL that is independent of NAD(P)H-oxidase-catalyzed formation of superoxide anion, because neither opsonized zymosan-stimulated CL nor the PMA-induced decrease in NAD (P)H-associated autofluorescence was affected by anti-My-26. In addition, ionomycin, over a wide concentration range, failed to generate any decrease in granulocyte autofluorescence. The A23187-induced CL inhibited by anti-My-26 was correlated with its depression of oxygen consumption. Furthermore, anti-My-26 was not cytotoxic and did not itself induce oxidative metabolism when used as a stimulant. Binding of anti-My-26 to phagocytic cells was not decreased by pre-exposure of cells to either A23187 or PMA. Evidence is presented to suggest that the binding of anti-My-26 to the granulocyte surface inhibits the oxidative response to calcium ionophore and PMA by blocking a common pathway(s) stimulated by these different secretagogues.     

Gentamicin and amikacin repress the growth of Plasmodium falciparum in culture, probably by inhibiting a parasite acid phospholipase

Human erythrocytes were loaded with either gentamicin or amikacin and subsequently infected with the human malarial parasite Plasmodium falciparum and grown in culture. Parasite invasion of erythrocytes was unaffected by the drugs, but subsequent development was retarded. The digestion of host cell cytosol in ring-stage parasites was inhibited by the drugs. A substantial acid, Ca2+-independent phospholipase activity could be monitored in parasite cytosol and was found to be inhibited by the drugs. These results imply that phospholipases are involved in the feeding mechanism of the parasite and that gentamicin and amikacin exert their inhibitory activity by affecting these enzymes.     

Methoxyindoles of the retina

Melatonin and other 5-methoxyindoles are compounds usually associated with the pineal gland. Research is expanding from studies of pineal melatonin to studies of extrapineal organs and of other 5-methoxyindoles besides melatonin. Research in recent years has shown that the retina also contains and synthetises 5-methoxyindoles. The biochemical modes of action are still unclear. Nevertheless, they seem to have physiological roles in the pineal gland and the retina. These compounds are thought to participate in the regulation of the cyclic metabolism of the retina. Melatonin and other 5-methoxyindoles are often classified as neuromodulators.     

Environmental factors affecting seasonal variation in immunity of clinically normal dogs

A whole blood lymphocyte stimulation test, an in vitro corollary of in vivo cell mediated immunity, was done with blood collected monthly from eleven dogs for a period of three years (August, 1977 through August, 1980). Seasonal variations in immunity were observed to occur. These fluctuations were analyzed for possible association with 22 environmental, solar, and meteorological parameters. Of the six independent variables significantly entering the predictive regression equations, sunspot activity (monthly mean daily number of sunspots) was most prominent, showing a significant negative correlation in 10 of the 11 dogs. This suggests that solar activity might be associated with some activity on earth, e.g., geomagnetism which in turn might affect immune response.     

Haematological correlates of burrowing in Ctenomys

Haematological parameters related to O2 transport and regulation of acid-base equilibrium were determined for two species of Ctenomys. The oxygen capacity values of Ctenomys blood are similar to those of other fossorial mammals. Ctenomys blood has almost half the number of red blood cells of Rattus blood but the amount of Hb in each blood cell is 2-2.5 times higher. Blood pH is within typical mammalian values. Concentration of inorganic phosphate is higher in Ctenomys than in rats while bicarbonate and protein values are within typical mammalian range.