Molecular species specificity of phospholipid breakdown in microsomal membranes of senescing carnation flowers

During senescence of cut carnation flowers, there is extensive breakdown of microsomal phospholipid. This is attributable, at least in part, to lipolytic activity associated directly with the microsomal membranes. Evidence indicating that one or more of the lipid-degrading enzymes in these membranes preferentially degrade phospholipid molecular species containing two diunsaturated acyl chains or at least one polyunsaturated acyl chain has been obtained by using radiolabeled phosphatidylcholine substrates. 16:0^*/16:0^*, 16:0/18:2^*, and 18:1^*/18:1^* phosphatidylcholine were degraded only minimally over a 3 hour period by microsomes isolated from senescing flowers. By contrast, [U-¹⁴C]phosphatidylcholine, which comprises various molecular species including those containing polyunsaturated acyl chains, and 18:0/20:4^* phosphatidylcholine were extensively degraded. Under identical conditions, but in the absence of added radiolabeled substrate, endogenous 18:2/18:2, 18:1/18:3, and 18:2/18:3 phosphatidylcholine were selectively depleted from the membranes. During natural senescence of the flowers, there was a sharp decline in microsomal 16:0/18:1 and 18:1/18:2 phosphatidylcholine, whereas molecular species containing two diunsaturated acyl chains or at least one polyunsaturated acyl chain remained unchanged or decreased only slightly. The data have been interpreted as indicating that provision of particular molecular species susceptible to lipase attack is a prerequisite to phospholipid catabolism in senescing membranes.     

Mammographic changes following reduction mammaplasty

Mammographic findings after reduction mammaplasty may be similar to those seen with carcinoma. A knowledge of the expected mammographic alterations would be helpful in differentiating postoperative changes from those seen with carcinoma of the breast. Accordingly, the clinical records and mammograms of patients who underwent reduction mammaplasty at the Dartmouth-Hitchcock Medical Center between March of 1977 and July of 1985 were analyzed. Forty-two patients had at least one mammographic examination following reduction mammaplasty. Periareolar soft-tissue changes and inferior pole alterations were present in almost all examinations of patients during the first 6 months after operation, but they decreased during the next few years. Asymmetrical densities were present in approximately half the patients throughout the follow-up period but decreased in degree. Parenchymal calcifications occurred later; few x-rays showed these calcifications during the first year, but 50 percent were apparent after 2 years. Evidence of fat necrosis occurred in approximately 10 percent. Four patients had biopsies for suspicious densities. Chronic inflammation and inclusion cyst were reported. We believe that changes after reduction mammaplasty are predictable and can usually be differentiated from those associated with cancer.     

Radiosensitization in multifraction schedules. I. Evidence for an extremely low oxygen enhancement ratio

Stable monolayers of contact-inhibited C3H 10T1/2 cells were used in multifraction radiation experiments to measure the oxygen enhancement ratio (OER) at low doses/fraction under conditions where cell cycle effects (repopulation, redistribution) were minimal. Consistent with there being a dose-dependent reduction in the OER at low doses, an extremely low OER of 1.34 was measured after 20 fractions of 1.7 Gy every 12 h. The sparing effects of fractionating radiation doses were not apparent for cells irradiated under hypoxic conditions (i.e., multifraction survivals were lower than acute single-dose values) until doses exceeding 15 Gy were reached. This result suggested a deficiency in the recovery from sublethal and/or potentially lethal damage might exist after hypoxic irradiations, thereby reducing the OER. The capacity to repair potentially lethal damage was found to be nearly the same after hypoxic as compared to aerobic irradiations. However, there was an apparent absence of sublethal damage repair by 10T1/2 cells between two hypoxic irradiations which could be a major contributing factor to the extremely low OER value measured in this multifraction schedule.     

Changing time perspective and mental health among Southeast Asian refugees

Little is known about the psychological mechanisms people employ in adapting to extreme circumstances such as becoming refugees. Case studies of refugees making up part of a sample of 1348 persons relocated from Southeast Asia to Vancouver, British Columbia, suggest that altering one's perception of time may be an adaptive strategy. During periods of acute stress, refugees seem to focus on the present to the relative exclusion of past and future. The reemergence of past and future into consciousness brings about a risk for developing depression. Epidemiological data corroborate inferences from case material, demonstrating that refugees are more present-oriented than the indigenous population. A Nostalgic time orientation, preoccupation with the past, is associated with elevated depression scores. Contrasts are drawn between nostalgia, a maladaptive pattern, and memory, which is an inevitable part of the process of personality integration.     

Construction of hybrid Tn501/Tn21 transposases in vivo: identification of a region of transposase conferring specificity of recognition of the 38-bp terminal inverted repeats.

In order to study the transposase enzymes of Class II prokaryotic transposable elements, we have constructed genes encoding hybrid transposase proteins. This was done by recombination in vivo between the tnpA genes of transposons Tn501 and Tn21. These hybrid genes can complement in trans a transposition-defective mutant of Tn501. The structures of the products of this complementation indicate whether the specificity of the hybrid transposase in recognising the 38 bp terminal inverted repeats is that of Tn501 or that of Tn21. The determinant of this specificity is in the N-terminal region of the transposase protein, between amino acids 28 and 216. The predicted amino acid sequences so far determined of transposases from the Class II family reveal an area of homology in this region.     

Binding of a nuclear factor to a consensus sequence in the 5' flanking region of zein genes from maize

The genomic organization of the zein structural genes and of regulatory loci influencing their expression suggests that control of zein gene expression will involve interactions between cis elements in the flanking DNA sequences and products from trans-acting genes. The interaction between fragments from the 5' flanking region of a zein gene and specific, double-stranded oligonucleotides with crude nuclear extracts from maize endosperm have been studied by nitrocellulose filter binding, gel retention and DNase I footprinting assays. Specific binding of a nuclear factor was observed and the exact position of the protein binding site was determined. The 22-nt binding site included 14 bp of a 15-bp sequence conserved in all zein genes.     

Proteoglycan metabolism associated with mouse metanephric development: morphologic and biochemical effects of beta-D-xyloside

Morphology and de novo incorporation of [35S]sulfate into proteoglycans were studied in fetal mouse kidneys at the onset of organogenesis. Branching morphogenesis and nephron development in organ culture and in vivo were associated with de novo synthesis of chondroitin-SO4 and heparan-SO4 proteoglycans. The role of proteoglycan metabolism in metanephrogenesis was then studied by analysis of the effects of p-nitrophenyl-beta-D-xylopyranoside (beta-D-xyloside) on renal development and proteoglycan metabolism. Incubation of fetal kidneys in beta-D-xyloside at concentrations of 1.0 and 0.5 mM, but not at 0.1 mM, caused inhibition of ureteric branching and markedly diminished synthesis of a large Mr 2.0 X 10(6) Da chondroitin-SO4 proteoglycan. Incorporation of [35S]sulfate was stimulated at all beta-D-xyloside concentrations, reflecting synthesis of xyloside initiated dermatan-35SO4 chains. In contrast to dramatic effects on chondroitin-SO4 synthesis and ureteric branching, beta-D-xyloside had no effect on heparan-SO4 synthesis or on development of the glomerulus and glomerular basement membrane. We thus characterize the proteoglycans synthesized early in the course of renal organogenesis and describe observations which suggest an association between metabolism of chondroitin-SO4 proteoglycan and development of the ureter.     

Locations of the hydrogenases of Methanobacterium formicicum after subcellular fractionation of cell extract.

The F420 hydrogenase of Methanobacterium formicicum was associated with membranes isolated by sucrose density gradient ultracentrifugation of cell extract. The methyl viologen hydrogenase was present in the soluble fractions. Column chromatography with phenyl-Sepharose CL-4B revealed that the F420 hydrogenase was strongly hydrophobic, suggesting that it associates with isolated membranes through hydrophobic interactions.     

The enzyme defect in bovine protoporphyria. Studies with purified ferrochelatase

Ferrochelatase was purified from the livers of normal and protoporphyria cattle by chromatography on Blue Sepharose CL-6B in order to investigate the enzyme defect in this disorder. The increase in specific activity (up to 2900-fold) indicated that the normal and protoporphyria enzymes were purified to a similar degree. The mutant enzyme had catalytic activity which was 10 to 15% of normal ferrochelatase, although the Michaelis constants for protoporphyrin and iron were similar. The molecular mass of the normal and protoporphyria enzyme protein was 40 kDa as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In the presence of 15 mM sodium cholate, gel filtration demonstrated a similar size. However, at a lower concentration of sodium cholate (4 mM) the molecular mass was about 240 kDa, suggesting that the purified enzymes aggregate under this condition. Polyvalent antibodies were raised in rabbits using as antigens purified normal native enzyme and normal 40-kDa protein which had been further purified by preparative SDS-PAGE. In Western blots these antibodies complexed with both the normal and mutant 40-kDa proteins. The amount of 40-kDa protein in normal and protoporphyria mitochondrial fractions was also similar as evaluated by Western blots. These studies indicate that the ferrochelatase defect in bovine protoporphyria probably results from a point gene mutation that causes a minor change in enzyme structure.