Hexokinase isoenzymes in diabetes

Hexokinase is present in the tissues in four isoenzymic forms. Cerebral tissue contains predominantly Type I hexokinase which is believed to be insulin-insensitive. In cerebral tissue about 60 to 70% of the hexokinase is bound to the particulate fraction. The changes in the distribution of hexokinase Type I and Type II together with the bound and free hexokinase have been studied in control, diabetic and diabetic animals treated with insulin. The results indicate that the presence of insulin is essential for the normal binding of the hexokinase to the particulate fraction. In heart tissue, Type II hexokinase bound to the pellet shows a significant decrease in diabetes, which is reversed on insulin administration.     

Microtubules and 10 nm-filaments in the retinal pigment epithelium during the diurnal light-dark-cycle

Summary Microtubules and 10 nm-filaments appear to be involved in the functions of the retinal pigment epithelium (RPE). The presence of microtubules in the RPE of light-adapted eyes, but not in dark-adapted eyes, suggests that they may be involved primarily in organelle movement. On the other hand, the random and constant presence of 10 nm-filaments within the basal portion of the PE implies a cytoskeletal role for these filaments.The authors thank their colleagues Pierre Couillard and Michel Anctil for helpful advice and criticism during the course of this study. Financial support was provided by the C.R.S.N.G. du Canada and the Ministère de l'Education du Québec (F.C.A.C.)     

The binding of berenil to Escherichia coli ribosome.

The binding of the nonintercalating dye berenil to the 70S ribosome of Escherichia coli has been demonstrated by spectrophotometric measurements and gel filtration through Biogel P100 column. The berenil spectrum is gradually shifted towards the red region with the increasing amount of ribosome added, the isosbestic point being at 375 nm. There is positive cooperativity in the binding of berenil to the ribosome as demonstrated by the equilibrium dialysis. On binding with berenil, the ribosome is degraded faster by RNase I especially at low Mg++ concentration and its capacity to inhibit RNase I catalysed hydrolysis of ribopolymers is decreased. These indicate the unfolding of the structure of the ribosome.     

Respiration,ATP level,and sugar accumulation in potato tubers during storage at 4°

A kinetic study was made of the relationship between respiration rate, sugar content and ATP levels, in fresh and aged potato tubers stored at 4°. The ATP content in tubers rose rapidly immediately after the chilling stress, while respiration rate decreased below the initial rate and sugar accumulation was not detected. After 4 days of storage, the ATP level declined and the sugars started to accumulate. The typical increase in respiration rate that usually follows chilling stress, appeared only in fresh tubers (at about the 6th day of storage). In dinitrophenol-treated tubers, the ATP level remained below the initial level and sugar accumulation was blocked completely. The evidence presented suggests that ATP elevation is not generated by the respiration burst.     

Effect of gibberellic acid treatment,and nutrient supply through detached tillers,upon haploid frequency in barley

Summary Haploids from Hordeum vulgare (2n = 14) X H. Bulbosum (2n = 14) crosses result after fertilization from the subsequent elimination of bulbosum chromosomes during early embryo development. Seed set from the cross is high but embryo culture is necessary to obtain seedlings. Application of gibberellin A₃ (GA₃) to pollinated florets was effective for increasing the frequency of haploid seedlings produced on both nutrient-fed detached tillers and intact plants. GA₃ increased both seed set and embryo yield. The number of cells per embryo during its transition to the haploid state was increased two to three times following GA₃ treatments. Enhanced embryo and endosperm development was attributed to increased mitotic activity. The number of visibly differentiated embryos was doubled to about 35 % of the cultured embryos after GA₃ was applied to detached tillers in nutrient solution. About 70 % of the resulting haploid plants developed from the visibly differentiated embryos. The detached tiller technique offers a convenient method of culturing haploids from field-grown plants.     

Studies on dehydro-l-ascorbic acid 2-arylhydrazone 3-oximes: Conversion into substituted triazoles and isoxazolines

l-threo-2,3-Hexodiulosono-1,4-lactone 2-(arylhydrazones) (2) were prepared by condensation of dehydro-l-ascorbic acid with various arylhydrazines. Reaction of 2 with hydroxylamine gave the 2-(arylhydrazone) 3-oximes (3). On boiling with acetic anhydride, 3 gave 2-aryl-4-(2,3-di-O-acetyl-l-threo-glycerol-l-yl)-1,2,3-triazole-5-carboxylic acid 5,4¹-lactones (4). On treatment of 4 with liquid ammonia, 2-aryl-4-(l-threo-glycerol-l-yl)-1,2,3-triazole-5-carboxamides (5) were obtained. Acetylation of 5 with acetic anhydride-pyridine gave the triacetates, and vigorous acetylation with boiling acetic anhydride gave the tetraacetyl derivatives. Periodate oxidation of 5 gave the 2-aryl-4-formyl-1,2,3-triazole-5-carboxamides (8), and, on reduction, 8 gave the 2-aryl-4-(hydroxymethyl)-1,2,3-triazole-5-carboxamides, characterized as the monoacetates and diacetates. Controlled reaction of 2 with sodium hydroxide, followed by neutralization, gave 3-(l-threo-glycerol-l-yl)-4,5-isoxazolinedione 4-(arylhydrazones), characterized by their triacetates. Reaction of 2 with HBr-HOAc gave 5-O-acetyl-6-bromo-6-deoxy-l-threo-2,3-hexodiulosono-1,4-lactone 2-(arylhydrazones); these were converted into 4-(2-O-acetyl-3-bromo-3-deoxy-l-threo-glycerol-l-yl)-2-aryl-1,2,3-triazole-5-carboxylic acid 5,4¹-lactones on treatment with acetic anhydride-pyridine.     

Mitochondrial DNA evolution in lagomorphs: Origin of systematic heteroplasmy and organization of diversity in European rabbits

Summary A characterization was conducted on mitochondrial DNA (mtDNA) molecules extracted separately from 107 European rabbits (Oryctolagus cuniculus) both wild and domestic, 13 European hares (Lepus capensis), and 1 eastern cottontail (Sylvilagus floridanus). Experimentally this study took into account restriction site polymorphism, overall length variation of the noncoding region, and numbers of repeated sequences. Nucleotide divergences indicate that the mtDNAs from the three species derived from a common ancestor some 6–8 million years (Myr) ago. Every animal appeared heteroplasmic for a set of molecules with various lengths of the noncoding region and variable numbers of repeated sequences that contribute to them. This systematic heteroplasmy, most probably generated by a rate of localized mtDNA rearrangements high enough to counterbalance the cellular segregation of rearranged molecules, is a shared derived character of leporids.The geographic distribution of mtDNA polymorphism among wild rabbit populations over the western European basin shows that two molecular lineages are represented, one in southern Spain, the second over northern Spain, France, and Tunisia. These two lineages derived from a common ancestor some 2 Myr ago. Their present geographical distribution may be correlated to the separation of rabbits into two stocks at the time of Mindel glaciation.Finally the distribution of mtDNA diversity exhibits a mosaic pattern both at inter- and intrapopulation levels.     

Extraction and analysis of superoxide free radicals (·O−2) from whole mammalian liver

Extraction of whole lobes of normal rat liver with dimethyl sulphoxide (DMSO) under N₂ gives extracts which contain 5—10 μmol/l·O^?₂ (50-100 nmol·O^?₂ per 10 ml extract per 4 g liver; 1.25-2.50 nmol·O^?₂ per millilitre per gram liver). Evidence for ·O^?₂ in the extracts is given by: (1) electron spin resonance signals (ESR), (2) differential pulse polarography (DPP), (3) chemiluminescence (CL), and (4) nitroblue tetrazolium reduction (NBT). All tests yield results identical with those obtained with authentic ·O^?₂. Extraction of ·O^?₂ is enhanced by tetrabutyl ammonium ion, and is maximal at 1-3 min. These results raise the possibility that substantial amounts of ·O^?₂ are normally sequestered in protective membranous sites in vivo.     

Primary structure of hemoglobin β-chain fromColumba livia (gray wild pigeon)

Primary structure of β-chain of pigeon is presented. It was determined by amino acid sequence analysis of intact β-chain and its peptides obtained by the enzymatic and chemical cleavage. Comparison of amino acid sequence of the chain with other available data shows β 14 Ile, β61 Lys, and β113 Ile as residues specific to pigeon. One important replacement at α₁β₁ contact is β55 Met→Ser.     

Brain Cytochrome Oxidase in Alzheimer''s Disease

A recent demonstration of markedly reduced (-50%) activity of cytochrome oxidase (CO; complex 4), the terminal enzyme of the mitochondrial enzyme transport chain, in platelets of patients with Alzheimer's disease (AD) suggested the possibility of a systemic and etiologically fundamental CO defect in AD. To determine whether a CO deficiency occurs in AD brain, we measured the activity of CO in homogenates of autopsied brain regions of 19 patients with AD and 30 controls matched with respect to age, postmortem time, sex, and, as indices of agonal status, brain pH and lactic acid concentration. Mean CO activity in AD brain was reduced in frontal (-26%: p less than 0.01), temporal (-17%; p less than 0.05), and parietal (-16%; not significant, p = 0.055) cortices. In occipital cortex and putamen, mean CO levels were normal, whereas in hippocampus, CO activity, on average, was nonsignificantly elevated (20%). The reduction of CO activity, which is tightly coupled to neuronal metabolic activity, could be explained by hypofunction of neurons, neuronal or mitochondrial loss, or possibly by a more primary, but region-specific, defect in the enzyme itself. The absence of a CO activity reduction in all of the examined brain areas does not support the notion of a generalized brain CO abnormality. Although the functional significance of a 16-26% cerebral cortical CO deficit in human brain is not known, a deficiency of this key energy-metabolizing enzyme could reduce energy stores and thereby contribute to the brain dysfunction and neurodegenerative processes in AD.