Linkage to Xq28 in a family with nonspecific X-linked mental retardation

Linkage analysis was performed in a family with nonspecific X-linked mental retardation (MRX). Affected individuals had no clinical characteristics other than mental retardation. Linkage was detected to the marker loci DXS477, DXS465, DXS52, DXS15 and F8C with maximum lod scores of 1.70, 1.32, 2.52, 1.70, and 1.09, respectively ( = 0.0). The results strongly indicate that the gene for mental retardation in the family studied maps close to DXS52.     

The borohydride-reducible compounds of human aortic elastin. Demonstration of a new cyclic amino acid in alkali hydrolysate, and changes with age and in patients with annulo-aortic ectasia including one with Marfan syndrome.

Chronic (10-day) diabetes was associated with increased metabolic flux through phenylalanine hydroxylase in isolated liver cells. This flux was stimulated by 0.1 microM-glucagon, but not by 10 microM-noradrenaline; 0.1 microM-insulin affected neither basal nor glucagon-stimulated flux. The increased rate of phenylalanine hydroxylation in diabetes was accompanied by parallel increases in enzyme activity (as measured with artificial cofactor) and immunoreactive-enzyme-protein content. In contrast with total protein synthesis, which decreased, phenylalanine hydroxylase synthesis persisted at the control rate in cells from diabetic animals. These findings are discussed in relation to the hormonal regulation of the hydroxylase and the known metabolic consequences of chronic diabetes.     

Normoxic and anoxic heat output of the freshwater bivalves Pisidium and Sphaerium

In fasting Pisidium amnicum and Sphaerium corneum, regular periods of behavioural and metabolic quiescence were shown to occur in the normoxic, constant environment of the flow-through chamber of a heat-flow microcalorimeter. The metabolic rate was suppressed to 7.5% of normal at 10° C and to 8.5–9.7% at 20° C for periods exceeding the period of active metabolism by a factor of 3.5 at 10° C and 8.3 at 20° C. The rate of heat output during normoxic quiescence was equal to that during environmental anoxia, suggesting spontaneous achievement of body anoxia by complete shell closure. The mass-specific integrated heat output during closure periods was independent of size. Parallel observations on clam behaviour suggested that metabolic quiescence coincided with shell closure, and bursts of heat flow with active ventilation. Shell closure was accompanied by pronounced bradycardia, down to 20% of the active rate. In a constant environment, the rhythmic quiescence is regulated by shell closure which is probably triggered by lack of food. Regular quiescence of fasting bivalves may conserve energy reserves considerably, the amount depending on the possible excretion rate of the end products, and the post-quiescence recovery costs, which were not measured. Heat output during the active period was close to the average metabolic rate found earlier for Sphaeriidae. However, all the values determined so far are likely to be underestimates of the natural metabolism because the effects of digestion and growth are not included.     

Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin

We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells.     

Determination of inorganic phosphate. A method for the determination of phosphatase activities by a continuous flow system

A sensitive and accurate method for the determination of inorganic phosphate is described. The method enables the estimation of 10 nanomoles of inorganic phosphate with a coefficient of variation of 3.6% for ten replicates. The method is suitable for the estimation of the activities of thiamine triphosphatase, adenosine triphosphatase, and alkaline and acid phosphatase by a continuous flow system.     

Alterations in osteoclast morphology following osteoprotegerin administration in the magnesium-deficient mouse

In the present study, we used osteoprotegerin (OPG), which blocks osteoclastogenesis, to correct and thus explain the hypercalcemia that is seen during dietary Mg deficiency in the mouse. Control and Mg-deficient mice received injections for 12 days of either OPG or vehicle only. Serum Ca was similar in Mg-deficient mice treated with OPG and in control mice receiving OPG (9.2±0.3 mg/dl vs. 9.2±0.5). Both groups had significantly higher serum Ca than controls or Mg-deficient animals receiving vehicle alone. Surprisingly, Mg-depleted mice that received OPG in doses that inhibit osteoclastic bone resorption remained hypercalcemic. Because mature osteoclasts still present in the marrow might be hyperactive, we examined osteoclast morphology at the light microscopic and ultrastructural level. Light microscopic examination of trabecular bone showed few osteoclasts in OPG-treated mice. Ultrastructural examination revealed that osteoclasts in OPG-treated mice have decreased contact with the endosteal bone surface and absence of a ruffled border. Because the morphology of the existing pool of mature osteoclasts did not enhance resorption, another mechanism, such as increased intestinal absorption of Ca in Mg-deficient mice, likely contributes to the hypercalcemia observed during Mg deficiency.     

Methylation: a regulator of HIV-1 replication?

Pakistan, the second most populous Muslim nation in the world, has started to finally experience and confront the HIV/AIDS epidemic. The country had been relatively safe from any indigenous HIV cases for around two decades, with most of the infections being attributable to deported HIV positive migrants from the Gulf States. However, the virus finally seems to have found a home-base, as evidenced by the recent HIV outbreaks among the injection drug user community. Extremely high-risk behavior has also been documented among Hijras (sex workers) and long-distance truck drivers. The weak government response coupled with the extremely distressing social demographics of this South-Asian republic also helps to compound the problem. The time is ripe now to prepare in advance, to take the appropriate measures to curtail further spread of the disease. If this opportunity is not utilized right now, little if at all could be done later.     

H+-pyrophosphatase of Rhodospirillum rubrum. High yield expression in Escherichia coli and identification of the Cys residues responsible for inactivation my mersalyl

H(+)-translocating pyrophosphatase (H(+)-PPase) of the photosynthetic bacterium Rhodospirillum rubrum was expressed in Escherichia coli C43(DE3) cells. Recombinant H(+)-PPase was observed in inner membrane vesicles, where it catalyzed both PP(i) hydrolysis coupled with H(+) transport into the vesicles and PP(i) synthesis. The hydrolytic activity of H(+)-PPase in E. coli vesicles was eight times greater than that in R. rubrum chromatophores but exhibited similar sensitivity to the H(+)-PPase inhibitor, aminomethylenediphosphonate, and insensitivity to the soluble PPase inhibitor, fluoride. Using this expression system, we showed that substitution of Cys(185), Cys(222), or Cys(573) with aliphatic residues had no effect on the activity of H(+)-PPase but decreased its sensitivity to the sulfhydryl modifying reagent, mersalyl. H(+)-PPase lacking all three Cys residues was completely resistant to the effects of mersalyl. Mg(2+) and MgPP(i) protected Cys(185) and Cys(573) from modification by this agent but not Cys(222). Phylogenetic analyses of 23 nonredundant H(+)-PPase sequences led to classification into two subfamilies. One subfamily invariably contains Cys(222) and includes all known K(+)-independent H(+)-PPases, whereas the other incorporates a conserved Cys(573) but lacks Cys(222) and includes all known K(+)-dependent H(+)-PPases. These data suggest a specific link between the incidence of Cys at positions 222 and 573 and the K(+) dependence of H(+)-PPase.