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.     

Bovine lens aldose reductase: identification of two enzyme forms

Two structurally different forms of bovine lens aldose reductase have been identified. Freshly prepared lens extracts contain an unactivated "b form" (ARb) which is sensitive to inhibition by Sorbinil. Upon incubation of the extracts with oxygen radical generating systems, ARb is converted to a more active "a form" (ARa), which is not inhibited by Sorbinil. ARa and ARb were purified to electrophoretic homogeneity.     

Change in stereospecificity of bovine lens aldose reductase modified by oxidative stress

Bovine lens aldose reductase (alditol:NADP+ oxidoreductase, EC 1.1.1.21) undergoes an oxidative modification, greatly stimulated by high ionic strength, upon incubation in the presence of oxygen radical generating systems (Del Corso, A., Camici, M., and Mura, U. (1987) Biochem. Biophys. Res. Commun. 148, 369-375). The enzyme modification is accompanied by a change in stereospecificity toward the two enantiomers of glyceraldehyde. In particular, the Km for L-glyceraldehyde of the native form increased over 150 times after the enzyme modification, with a decrease in the catalytic efficiency of over 200 times. By contrast, for the D-enantiomer the Km increased only 7 times with respect to the native form, with a concomitant decrease in the catalytic efficiency of only approximately 3 times. This dramatic change in stereospecificity may account for the reported apparent cooperative behavior exhibited also by highly purified electrophoretically homogeneous preparations of aldose reductase.     

Patterns of Root Colonization in Epacridaceous Plants Collected from Different Sites

Root colonization was studied in ten species of the Epacridaceaeat three sites in Victoria by morphological and cross-inoculationexperiments. The sites and genera chosen were Cranbourne [Epacrisimpressa Labill. andLeucopogon ericoides(Smith) R. Br.] andRye [L. parviflorus(Andrews) Lindley] on the Mornington Peninsula,and the Grampians[Astroloma conostephioides(Sond.) Benth.,A.humifusum(Cav.) R. Br.,A pinifolium(R. Br.) Benth,Brachylomadaphnoides(Smith) Benth.,E. impressa, E. impressavar.grandifloraBenth.andStyphelia adscendensR. Br.] in western Victoria. For morphologicalstudies, samples of roots from each species at each site werecleared and stained and examined microscopically. For cross-inoculationstudies, cuttings from each site were struck in potting mediuminoculated with soil from the same and other sites. The ericoidmycorrhizae in the roots of plants found at or grown in Cranbourneand Rye soils were similar. Both were significantly differentfrom the internal hyphae found in the roots of plants foundat or grown in Grampians soils, which were three times largerin diameter and formed dense coils which filled the host celland invaded adjacent epidermal cells. This suggests that morethan one fungus is involved in the relationships, that the MorningtonPeninsula sites had a different fungus from the Grampians siteand that host specificity is low. Vesicular structures werealso found commonly on plants at the Grampians site, in contrastwith other sites. Epacridaceae; root; fungus; mycorrhiza; morphology; inoculation     

Intra- and inter-specific relationships in the six Italian species of the fairy shrimp genus Chirocephalus: combining allozyme and mtDNA data

This study analysed the levels of genetic differentiation within and among the six Italian species of the fairy shrimp genus Chirocephalus by analysing electrophoretic polymorphisms at 22 enzymatic loci and by sequencing a 665‐bp fragment of the mitochondrial gene encoding for subunit I of cytochrome oxidase. The allozyme data revealed different levels of intra‐specific differentiation; mean θ estimates were low in Chirocephalus salinus, higher and comparable in C. diaphanus and C. kerkyrensis, while C. ruffoi was the most genetically structured species. At the inter‐specific level, C. marchesonii was the most differentiated species, both for allozymes and mtDNA. Phylogenetic relationships deduced from allozymes and mtDNA were not always consistent with each other. This highlights the differences in performance of the two classes of molecular markers and the need of different independent strategies of data analysis to search for possible incongruence. Neither allozymes nor mtDNA supported monophyly of the diaphanus‐group, previously recognized on the basis of the morphology of appendages (antennae and penes). In contrast the molecular results were consistent with the great heterogeneity in resting egg morphology among representatives of the diaphanus‐group.     

In situ inactivation of E. coli uridylylation cycle is independent of the state of covalent modification of the components of the glutamine synthetase cascade

Permeabilization of nitrogen-starved cells of Escherichia coli W with Lubrol WX leads to a selective inactivation of the uridylyl-removing uridylyltransferase (UR/ UTase) enzyme of the glutamine synthetase (GS) cascade system; whereas similar treatment does not affect activity of UR/UTase in cells grown under conditions of nitrogen excess (10 mm glutamine) (Mura, U., and Stadtman, E. R. (1981) J. Biol. Chem.256, 13014–13021). The possibility that susceptibility to Lubrol inactivation is related to differences in the state of adenylylation of GS and/or in the state of uridylylation of the P_II protein was investigated. Permeabilized cells from nitrogen sufficient as well as from nitrogen-limited growth medium were exposed to Lubrol after prior incubation under conditions that lead to high or low states of GS adenylylation and high or low P_IID/P_IIA ratios. Integrity of UR/UTase was monitored by measuring the capacity of UTP to stimulate the deadenylylation of GS in situ. The results showed that the inactivation of UR/UTase by Lubrol is not affected by the states of GS adenylylation or P_II uridylylation.     

Preliminary characterization of adenosine deaminase from Bacillus cereus

Adenosine deaminase from Bacillus cereus is quite unstable, similarly to other bacterial deaminases, but it shows a peculiar stabilizing effect by some monovalent cations. These include K+, Li+, NH4+ and to a lesser extent Cs+. Maximal stabilization of the deaminase is exerted by K+ at concentrations higher than 20 mM. The enzyme can be rapidly inactivated by sulphydryl reagents such as p-hydroxymercuribenzoate. Since adenosine deaminase from B. cereus, in addition to monovalent cations, is stabilized also by dithiothreitol, a possible influence of monovalent cations on the reactivity of some sulphydryl groups on the enzyme has been suggested.     

Premature induction of amylase in pancreas and parotid gland of growing rats by dexamethasone

Studies were made on changes in the contents of α-amylase (EC 3.2.1.1) in the pancreas and parotid gland of rats during postnatal devlopment, on the premature induction of this enzyme by hormones and on the existence of specific glucocorticoid receptors in these tissues.The amylase content in the pancreas increased from the 9th day after birth and reached the adult level on the 28th day, its content in the parotid gland increased rapidly from the 16th to 28th day after birth and then rose more gradually to the adult level.Injection of dexamethasone into rats 6–8 days after birth induced increase in the amylase of the pancreas but not the parotid gland. However, injection of dexamethasone into weanling rats 21–23 days after birth resulted in precocious induction of amylase in both tissues.Specific glucocorticoid receptors were detectable in the parotid gland of rats from 6 days after birth but were almost undetectable in the pancreas until adolescence.