Lack of an Efficient Endoplasmic Reticulum-localized Recycling System Protects Peroxiredoxin IV from Hyperoxidation

Typical 2-Cys peroxiredoxins are required to remove hydrogen peroxide from several different cellular compartments. Their activity can be regulated by hyperoxidation and consequent inactivation of the active-site peroxidatic cysteine. Here we developed a simple assay to quantify the hyperoxidation of peroxiredoxins. Hyperoxidation of peroxiredoxins can only occur efficiently in the presence of a recycling system, usually involving thioredoxin and thioredoxin reductase. We demonstrate that there is a marked difference in the sensitivity of the endoplasmic reticulum-localized peroxiredoxin to hyperoxidation compared with either the cytosolic or mitochondrial enzymes. Each enzyme is equally sensitive to hyperoxidation in the presence of a robust recycling system. Our results demonstrate that peroxiredoxin IV recycling in the endoplasmic reticulum is much less efficient than in the cytosol or mitochondria, leading to the protection of peroxiredoxin IV from hyperoxidation.     

Promoting Smoke-Free Homes: A Novel Behavioral Intervention Using Real-Time Audio-Visual Feedback on Airborne Particle Levels

Interventions are needed to protect the health of children who live with smokers. We pilot-tested a real-time intervention for promoting behavior change in homes that reduces second hand tobacco smoke (SHS) levels. The intervention uses a monitor and feedback system to provide immediate auditory and visual signals triggered at defined thresholds of fine particle concentration. Dynamic graphs of real-time particle levels are also shown on a computer screen. We experimentally evaluated the system, field-tested it in homes with smokers, and conducted focus groups to obtain general opinions. Laboratory tests of the monitor demonstrated SHS sensitivity, stability, precision equivalent to at least 1 µg/m³, and low noise. A linear relationship (R² = 0.98) was observed between the monitor and average SHS mass concentrations up to 150 µg/m³. Focus groups and interviews with intervention participants showed in-home use to be acceptable and feasible. The intervention was evaluated in 3 homes with combined baseline and intervention periods lasting 9 to 15 full days. Two families modified their behavior by opening windows or doors, smoking outdoors, or smoking less. We observed evidence of lower SHS levels in these homes. The remaining household voiced reluctance to changing their smoking activity and did not exhibit lower SHS levels in main smoking areas or clear behavior change; however, family members expressed receptivity to smoking outdoors. This study established the feasibility of the real-time intervention, laying the groundwork for controlled trials with larger sample sizes. Visual and auditory cues may prompt family members to take immediate action to reduce SHS levels. Dynamic graphs of SHS levels may help families make decisions about specific mitigation approaches.     

Structure and variability of mammalian peroxisomal membrane proteins.

Peroxisomal membrane proteins (PMPs) from the Swiss-Webster mouse are analyzed and compared to those of rats and humans using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. A purification procedure for fresh mouse, rat, or human biopsy liver which enriches peroxisomal/mitochondrial marker enzyme ratios over 100-fold is characterized. When analyzed by SDS-PAGE, membranes of purified liver peroxisomes are shown to contain the same complement of 145-, 70-, 55-, 36-, and 22-kDa PMPs in rats, mice, and humans. A rabbit polyclonal antibody raised against mouse peroxisomal membranes demonstrates immunoreactivity to 145- and 70-kDa proteins in fresh liver homogenates from all three species and in control or Zellweger syndrome fibroblasts from humans. Human autopsy or placental tissues which were refrigerated before analysis exhibited 105-, 55-, and 36-kDa peptides which may be derived from the 145- and 70-kDa peptides. Such conversions, if related to degradation, may explain difficulties in purifying peroxisomes from human autopsy specimens. Variable amounts of the 55-kDa peptide also occurred in mouse adrenal and lung, and the conversion of higher to lower molecular weight PMPs could not be demonstrated by in vitro incubation of mouse liver. Further definition of the structure and variability of mammalian PMPs should be helpful in understanding polyenzymopathies such as Zellweger syndrome.     

Different pathways of [3H]inositol phosphate formation mediated by alpha 1a- and alpha 1b-adrenergic receptors

The types of inositol phosphates (InsPs) formed in response to activation of alpha 1-adrenergic receptor subtypes were determined in collagenase-dispersed renal cells and hepatocytes by high pressure liquid chromatography separation. In hepatocytes, which contain only the alpha 1b subtype, norepinephrine stimulated rapid (10-s) formation of [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4)P3 and slower (5-min) formation of Ins(1,4)P2 and Ins(1)P. Selective inactivation of alpha 1b receptors by chloroethylclonidine almost completely blocked the effects of norepinephrine in hepatocytes. In renal cells, which contain both alpha 1a and alpha 1b receptors in a 60:40 ratio, norepinephrine did not significantly increase the size of any peaks until 5 min after agonist activation. At this time, only a peak eluting with Ins(1)P and one eluting shortly after Ins(1,4)P2 were significantly elevated. Incubation with norepinephrine for 2 h caused small but significant increases in peaks co-eluting with Ins(1)P and Ins(1,4,5)P3 in renal cells; however, only the increase in Ins(1)P was inhibited by chloroethylclonidine pretreatment. Extraction under neutral conditions suggested that cyclic InsPs may be the primary compounds formed in response to norepinephrine in renal cells. Removal of extracellular Ca2+ caused a 60% reduction in the InsP response to norepinephrine in renal cells but had no effect in hepatocytes. These results suggest that activation of alpha 1a and alpha 1b receptor subtypes results in formation of different InsPs and that the response to alpha 1a activation may require influx of extracellular Ca2+.