The Prion Protein Preference of Sporadic Creutzfeldt-Jakob Disease Subtypes

Sporadic Creutzfeldt-Jakob disease (CJD) is the most prevalent manifestation of the transmissible spongiform encephalopathies or prion diseases affecting humans. The disease encompasses a spectrum of clinical phenotypes that have been correlated with molecular subtypes that are characterized by the molecular mass of the protease-resistant fragment of the disease-related conformation of the prion protein and a polymorphism at codon 129 of the gene encoding the prion protein. A cell-free assay of prion protein misfolding was used to investigate the ability of these sporadic CJD molecular subtypes to propagate using brain-derived sources of the cellular prion protein (PrP^C). This study confirmed the presence of three distinct sporadic CJD molecular subtypes with PrP^C substrate requirements that reflected their codon 129 associations in vivo. However, the ability of a sporadic CJD molecular subtype to use a specific PrP^C substrate was not determined solely by codon 129 as the efficiency of prion propagation was also influenced by the composition of the brain tissue from which the PrP^C substrate was sourced, thus indicating that nuances in PrP^C or additional factors may determine sporadic CJD subtype. The results of this study will aid in the design of diagnostic assays that can detect prion disease across the diversity of sporadic CJD subtypes.     

The effect of ingesting a saltbush and barley ration on the carcass and eating quality of sheepmeat

Forage halophytes such as saltbush (Atriplex spp.) are widely used to revegetate Australian saline land and can provide a medium-quality fodder source. An animal house experiment was conducted to investigate differences in the carcass and eating quality of sheep ingesting saltbush from saline land in combination with a barley supplement. Twenty-six merino hoggets (two groups of 13) were fed either a 60 : 40 dried saltbush (Atriplex nummularia): barley (S + B) ration or a 33 : 25 : 42 lupins : barley : oaten hay ration (C) for 10 weeks prior to commercial slaughter. After 10 weeks, all sheep were commercially slaughtered and a single loin (from 12th rib to chump) collected from each animal for taste-panel analysis. Carcass weight, total tissue depth over the 12th rib 110 mm from the midline (GR fat depth), ultimate pH and colour were determined and X-ray bone densitometry used to estimate the fat content of the carcass. Blood samples were taken to assess the hormonal response to ingesting these diets and fatty acid profiles of the subcutaneous and intramuscular fat were determined. Both groups grew at the same rate (62 g/day) and had similar hot carcass weights (P > 0.01) (17.2 ± 0.3 kg for S + B and 17.9 ± 0.3 kg for C). However, these live weights may not be high enough to be commercially viable such that saltbush and barley may only be suitable as a maintenance feed. The S + B-fed sheep had a significantly (P = 0.055) lower fat and higher lean content (P < 0.05) than the C group. This is a positive finding as fat denudation is a significant cost to processors and farmers can produce sheep that are depositing less fat or more lean per unit of live-weight gain. The decreased fat and increased lean content were attributed to the higher protein : energy ratio available for production and lower circulating insulin and higher growth hormone of the S + B-fed sheep. The lower body-fat content and lower metabolisable energy and digestible organic matter intake did correlate with the sheep fed the S + B diet, having a significantly lower percentage of unsaturated fat and equal levels of saturated fat than the C treatment. Diet had no effect on the ultimate pH or colour of the meat. Treatment had no significant effect on any of the eating-quality attributes (P > 0.1). The drying of the saltbush, the shorter length of the experimental period and the low carcass fat content were believed to have contributed to this result. Further field experiments are needed to clarify the benefits to carcass and eating quality of ingesting saltbush.     

Microenvironmental factors and the binding of glycolytic enzymes to contractile filaments.

1. In reviewing the microenvironmental factors involved in the binding of the glycolytic enzymes to contractile filaments, consideration has been given to the significance of molecular crowding in maintaining these interactions under cellular conditions, and the influence of hormones, metabolites, pH and enzyme modifications on these phenomena. 2. Overall, these data serve to emphasize the biological reality of these associations, and their micro-organizational adaptations during physiological activities.     

Zinc content of Escherichia coli-expressed constitutive isoforms of nitric-oxide synthase. Enzymatic activity and effect of pterin.

Recently, we obtained x-ray crystallographic data showing the presence of a ZnS4 center in the structure of Escherichia coli-expressed bovine endothelial nitric-oxide synthase (eNOS) and rat neuronal nitric-oxide synthase (nNOS). The zinc atom is coordinated by two CXXXXC motifs, one motif being contributed by each NOS monomer (cysteine 326 through cysteine 331 in rat nNOS). Mutation of the nNOS cysteine 331 to alanine (C331A) results in the loss of NO. synthetic activity and also results in an inability to bind zinc efficiently. Although prolonged incubation of the C331A mutant of nNOS with high concentrations of L-arginine results in a catalytically active enzyme, zinc binding is not restored. In this study, we investigate the zinc stoichiometry in wild-type nNOS and eNOS, as well as in the C331A-mutated nNOS, using a chelation assay and electrothermal vaporization-inductively coupled plasma-mass spectrometry. The data reveal an approximate 2:1 stoichiometry of heme to zinc in (6R)-5,6,7,8-tetrahydro-L-biopterin-replete, wild-type nNOS and eNOS and show that the reactivated C331A mutant of nNOS has a limited ability to bind zinc. The present study substantiates that the zinc in NOS is structural rather than catalytic and is important for maintaining optimally functional, enzymatically active, constitutive NOSs.     

Insulin-like growth factor I receptors in neuronal and glial cells. Characterization and biological effects in primary culture

Primary cultures of neuronal and glial cells from 1-day-old neonatal rats contain high affinity receptors for insulin-like growth factor I (IGF-I). The IC50 for displacement of 125I-IGF-I binding by unlabeled IGF-I was 3 nM for neuronal cells and 4 nM for glial cells. Unlabeled insulin was 20-50 times less potent. Apparent molecular mass of the alpha subunits of the IGF-I receptor was 125 kDa in neuronal and 135 kDa in glial cells. IGF-I induced autophosphorylation of the IGF-I receptor beta subunit in lectin-purified membrane preparations in a dose-dependent manner. The major phosphoamino acid of the beta subunit in both cell types was tyrosine in the IGF-I-stimulated state and serine in the basal state. Apparent molecular mass of the beta subunits of the IGF-I receptors was 91 kDa for neuronal and 95 kDa for glial cells. Tyrosine kinase activity of the IGF-I receptors was demonstrated by IGF-I-induced phosphorylation of the exogenous substrate poly(Glu, Tyr) 4:1 in both cell types. IGF-I had no effect on 2-deoxyglucose uptake in neuronal cells. In contrast, in glial cells, IGF-I stimulated 2-deoxyglucose uptake at very high doses, presumably acting via the insulin receptor. The effect of IGF-I as a neurotrophic growth factor in both neuronal and glial cells was demonstrated by its stimulation of [3H]thymidine incorporation. These findings suggest the IGF-I is an important growth factor in nervous tissue-derived cells.     

AP endonuclease and uracil DNA glycosylase activities in Deinococcus radiodurans.

An endonuclease specific for apurinic/apyrimidinic (AP) sites was identified and purified from extracts of Deinococcus radiodurans. The enzyme is 34.5 kD, has no activity towards normal, alkylated, uracil-containing, or UV-irradiated DNA, and is active in the presence of EDTA. The addition of up to 10 mM Mg2+ or Mn2+ did not affect activity, but higher concentrations were inhibitory. There is no associated exonuclease activity, either in the presence or absence of divalent cation. Optimal reaction conditions were 150 mM NaCl and pH 7.5. A uracil DNA glycosylase was also detected, active in the presence of EDTA, selectively removing uracil from DNA without generating other byproducts. The optimal reaction conditions were 50 mM NaCl and pH 7.5. Implications for base excision repair in D. radiodurans are discussed.