Sequence analysis of ripening-related cytochrome P-450 cDNAs from avocado fruit

The ripening of avocado fruit is associated with the expression of a number of mRNAs concomitant with overt changes in texture and flavor. Two overlapping cDNAs for a mRNA that accumulates during ripening were identified. Sequence analysis of these two cDNAs revealed a polypeptide of 471 amino acids with characteristics of a typical P-450: an N-terminal hydrophobic membrane anchor, a conserved heme-binding domain in the C-terminal region, and patches of similarity to various P-450 family members. Further evidence that this polypeptide represents a cytochrome P-450 oxidase comes from the recent isolation and characterization of a cytochrome P-450 from ripe avocado mesocarp [O'Keefe, D. P. & Leto, K. J. (1989) Plant Physiol. 89, 1141-1149]. The N terminus of the predicted polypeptide in the cDNAs is identical to the N terminus of the purified avocado P-450. Gel blot analysis of RNA from fruit at various stages of ripening showed the accumulation of an 1800-nucleotide P-450 mRNA that hybridized to the P-450 cDNA. The P-450 protein predicted by the avocado cDNA sequence shares less than 40% positional identity with any known P-450 gene family. We propose therefore that it be placed in a separate family, P450LXXI, and that the corresponding gene from avocado be named cyp71A1.

[Evaluation of RPHA fecal occult blood test in screening for colorectal cancer]

Evaluation of reverse passive hemagglutination (RPHA) fecal occult blood (FOB) test in screening for colorectal cancer was carried out in a group of subjects (3034 persons) with history of rectal polyp and ulcer. All subjects were examined by 60 cm fiberoptic colonoscopy, RPHA and benzidine (BT) FOB tests. Among this high risk population, 10 cases of colorectal cancer and 1 case of rectal carcinoid were detected by colonoscopy and pathology. Regarding the findings under fiberoptic colonoscopy as a reference standard, the sensitivity of RPHA and BT in screening for colorectal cancer was 63.6% and 72.7%; the specificity was 81.9% and 61.7%; the general indicator--Youden index was 0.46 and 0.34, respectively. In 7 cases of colorectal cancer with both FOB tests positive, 5 (71%) had lesions in early stages (Dukes A and B). The results indicate that comparing with BT, RPHA has slightly lower sensitivity but higher specificity. RPHA fecal occult blood test could be used as preliminary screening for colorectal cancer.

cDNA sequence for human erythrocyte ankyrin

The cDNA for human erythrocyte ankyrin has been isolated from a series of overlapping clones obtained from a reticulocyte cDNA library. The composite cDNA sequence has a large open reading frame of 5636 base pairs (bp) with the complete coding sequence for a polypeptide of 1879 amino acids with a predicted molecular mass of 206 kDa. The derived amino acid sequence contained 194 residues that were identical to those obtained by direct amino acid sequencing of 11 ankyrin proteolytic peptides. The primary sequence contained 23 highly homologous repeat units of 33 amino acids within the 90-kDa band 3 binding domain. Two cDNA clones showed evidence of apparent mRNA processing, resulting in the deletions of 486 bp and 135 bp, respectively. The 486-bp deletion resulted in the removal of a 16-kDa highly acidic peptide, and the smaller deletion had the effect of altering the COOH terminus of the molecule. Radiolabeled ankyrin cDNAs recognized two erythroid message sizes by RNA blot analysis, one of which was predominantly associated with early erythroid cell types. An ankyrin message was also observed in RNA from the human cerebellum by the same method. The ankyrin gene is assigned to chromosome 8 using genomic DNA from a panel of sorted human chromosomes.

Prevalence survey of cytomegalovirus infection in children in Chengdu

Cytomegalovirus (CMV) is a common worldwide perinatal infection. Although usually asymptomatic, it may cause deafness in up to 15% of these infants. A cross-sectional study was performed to determine the age-specific prevalence of CMV seropositivity in Chinese children and to determine if any risk factors for infection could be identified. In a two-stage sampling procedure, nine districts were randomly selected from 70 citizenship districts in Chengdu, Sichuan Province, People's Republic of China. Then, 1,950 households were randomly selected from 11,886 households and interviewed. Blood was obtained from all children aged less than seven years and assayed using an enzyme-linked immunosorbent assay method. A subgroup of sera was retested at the research laboratory and also sent to the National Reference Laboratory in Beijing. Kappa values for the test agreement with the reference laboratory and retesting within the study laboratory were 0.94 and 0.86, respectively. Seropositivity averaged 52% in those aged less than one year and 60% in those between four and seven years. A higher rate of seropositivity was observed in urban versus rural children (odds ratio (OR) = 2.55), breast feeding in urban areas only (OR = 1.87), and day care versus home care setting (OR = 1.59). High CMV seroprevalence, even in the first year of life, was observed in this population of well children in Chengdu, China. An association was observed between seroprevalence and residence, method of feeding, and day care attendance.

Selective killing of tumor cells in vitro by an immunotoxin composed of ricin and monoclonal antibody against Ia antigen

A monoclonal antibody (MAb-HB55) directed against a HLA class II antigen (Ia), was purified by DE-52 chromatography. The purified MAb contained less than 5% impure protein detected by SDS-PAGE. Ricin was conjugated with the MAb via a disulfide bond to construct an immunotoxin (ricin-HB55). The concentration causing fifty percent growth inhibition (IC50) was 2 x 10(-11)M for the Raji cells. In contrast, the IC50 for Molt-4 and K562 cells was 100 times higher than that for the Raji cells. B lymphocytes separated from peripheral blood lymphocytes by nylon wool were selectively killed by the conjugate, but T lymphocytes were not apparently affected. Our results demonstrate that the immunotoxin is selectively cytotoxic to Raji cells and B-cells, and may have potential for purging malignant cells from bone marrow of patients with B-cell leukemia and lymphoma.

Role of the octamer motif in hybrid cell extinction of immunoglobulin gene expression: extinction is dominant in a two enhancer system

We have shown previously that genes activated by the immunoglobulin heavy chain (IgH) enhancer or promoter in mouse myeloma cells are extinguished upon fusion of the myeloma with a mouse T cell lymphoma. Here we show that the conserved octamer sequence shared by the IgH enhancer and promoter, when multimerized to form a tissue-specific enhancer, can also render a gene extinguishable under the same experimental conditions. Extinction, however, is not correlated with either absence of the tissue-specific transcription factor OTF-2 or loss of its ability to bind the octamer sequence. It was also found that extinction mediated by the IgH enhancer is dominant to transcriptional activation by the SV40 enhancer. We propose, therefore, that the T cell-negative regulator responsible for IgH gene extinction does not simply prevent IgH enhancer activation but interferes with gene expression more directly, perhaps by disrupting the transcription complex established as a result of tissue-specific enhancer activation.

Adrenergic receptors mediate changes in c-fos mRNA levels in brain

Recent evidence supports a role for transient c-fos expression as one step in signalling pathways by which membrane receptor-ligand interactions are transduced into appropriate intracellular responses. The activity of adrenergic receptors is mediated by second messenger systems which include ion fluxes, changes in cAMP concentration and enhanced phosphoinositide turnover. In order to determine if C-fos induction was also a step in adrenergic signal transduction in the brain, we performed in vivo studies with drugs specific for different adrenergic receptor types. Unexpectedly, we found that the stress associated with a single intraperitoneal (i.p.) injection of drug vehicle produced a transient increase (averaging 4.0-fold) in c-fos mRNA levels in rat brain. Injection of the alpha 2-adrenoreceptor antagonist, yohimbine, produced a transient increase which was larger in magnitude (averaging 9.6-fold) and longer in duration than that produced by injection of the drug vehicle alone. In experiments designed to ask whether either of these inductions was mediated by specific types of adrenergic receptors, we found that the alpha 2- and beta-adrenoreceptors were involved in both responses, while the alpha 1-receptor played a role in mediating the yohimbine induction, but no detectable role in the solvent induction. One hypothesis consistent with our results is that the norepinephrine (NE) released due to the stress associated with an i.p. injection interacts with postsynaptic beta-adrenergic receptors, resulting in the observed c-fos mRNA induction. When the negative feedback effect of NE, mediated by presynaptic alpha 2-receptors, is blocked by yohimbine, the postsynaptic response is enhanced and prolonged.

Vanadate activation of bromoperoxidase from Corallina officinalis

A nonheme bromoperoxidase has been purified to homogeneity from the red seaweed Corallina officinalis. Like the corresponding enzyme previously reported from C. pilulifera, this bromoperoxidase contains a significant amount of nonheme iron. However, it is vanadate ion and not iron that activates the enzyme, and maximal activity is achieved with stoichiometric vanadium incorporation. The absence of competition between vanadium and iron suggests that they occupy distinct binding sites in the protein. A correlation between vanadium content and catalytic activity indicates that less than 12 percent of the maximal activity of the enzyme can be derived from metals other than vanadium.

Cigarette smoking, alcohol consumption and primary liver cancer: a case-control study in the USA

Cigarette smoking and alcohol consumption were examined as potential risk factors in a case-control study of primary liver cancer (PLC). A total of 165 PLC cases and 465 matched controls from several US hospitals were studied. A weak but statistically significant (p less than 0.05) dose-response relationship was observed between alcohol consumption and PLC in elderly females independent of other major risk factors (adjusted OR = 1.87 and 3.48 for 1-2 and greater than 3 drinks per day, respectively) and a similar trend was evident in elderly males. The risk for PLC was also elevated in elderly females who were current cigarette smokers (adjusted OR = 3.30). Our results suggest that alcohol consumption and cigarette smoking may have minor age- and sex-specific effects on the development of PLC, and underscore the need for further investigations to elucidate major PLC risk factors in US populations.

Distribution of Clostridium botulinum in Japan and in Shinkiang district of China

Soil specimens obtained from several areas of Japan, which are closely located to or facing the Continental land of China, were examined for the distribution of Clostridium botulinum, especially pertaining to types A and B. A total of 266 specimens of Japan, when cultured, showed no type A or B toxicity, although 30 (11.3%), 4 (1.5%), and 10 (3.8%) of the specimens showed C1, C2, and type E toxicities, respectively. On the contrary, types A and/or B toxicities were shown, by the same method, in 14 of 20 specimens of Shinkiang district, China. The highest number of C. botulinum cells found in one gram of soil specimen was 25 for type A and 10 for type B.

Genes activated in the presence of an immunoglobulin enhancer or promoter are negatively regulated by a T-lymphoma cell line

The tissue-specific expression of immunoglobulin genes can be partially explained by a requirement for activating factors found only in B lymphocytes and their derivatives. However, loss of immunoglobulin expression upon fusion of an immunoglobulin-producing myeloma cell with a T lymphoma cell (BW5147) or fibroblast (L cell) suggests that negatively acting factors also play a role in the tissue specificity of immunoglobulin genes. Expression of a cloned immunoglobulin heavy-chain gene introduced into myeloma cells was suppressed after fusion of the myeloma transformants with BW5147. The presence of either the immunoglobulin heavy-chain enhancer or promoter conferred suppression, under similar conditions, upon a heterologous gene that is normally expressed in both B and T lymphocytes. These immunoglobulin heavy-chain gene control regions, or gene modifications induced by them, are subject to negative control by T-lymphocyte-derived factors.

T cell recognition of endogenous IgG2a expressed in B lymphoma cells

We recently characterized a panel of C57BL/6J T cell clones specific for IgG2a of the a allotype in association with I-Ab. Several of the clones gave surprisingly strong responses in the presence of normal spleen cells from several H-2b strains, including C3H.SW, A.BY, D1.LP and BALB.B, without the addition of exogenous antigen. Experiments using Igh-congenic mouse strains demonstrated that this response was directed towards shared allotypic determinants expressed on endogenously synthesized IgG2a molecules in various strains. Here we present evidence that the cell(s) responsible for this stimulation are conventional low density splenic accessory cells. Presentation of endogenously synthesized IgG2a by this population of dendritic cells, macrophages, and/or activated B cells was chloroquine sensitive. Thus, we conclude that this response is probably directed towards secreted IgG2a molecules that are internalized, processed and re-expressed at the cell surface in association with class II molecules. We also tested the ability of T cell clone B61-34 to respond in the presence of the B lymphoma cell line M12.C3.A2. A strong response was again observed in the absence of exogenous antigen. Northern gel analysis of M12.C3.A2 messenger RNA provided evidence that these cells synthesize IgG2a in both a secreted and a membrane form. The response directed towards endogenous IgG2a expressed in M12.C3.A2 lymphoma cells is chloroquine resistant and considerably more efficient than that stimulated by IgG2a added as exogenous soluble antigen. These results demonstrate for the first time that B cells have the capacity to present antigenic determinants expressed on endogenously synthesized immunoglobulins to class II-restricted T cells. The implications of these findings with respect to network models of immune regulation are discussed.

Case-control study of prostate cancer and socioeconomic factors

A total of 1,162 prostate cancer cases and 3,124 age-matched hospital controls from several U.S. hospitals were studied to identify associations between prostate cancer and life-style variables. Among white males, college education, professional occupation, and non-Jewish ethnicity were weakly associated with the risk of prostate cancer (ORs = 1.5, 1.8, and 1.3, respectively, P less than 0.01). These relationships retained statistical significance after adjustment for age, marital status, body mass, cigarette smoking, alcohol consumption, and physical activity in multiple logistic regression models. Among black males, similar, though nonsignificant, risk elevations were observed for education and occupation. Weak positive effects of borderline statistical significance were observed for high body mass, low physical exercise, and high serum cholesterol (in elderly males only), and a significant reduction in risk was noted for never married black males. Cigarette smoking and alcohol consumption were not related to the risk of prostate cancer.

DNA rearrangement causes a high rate of spontaneous mutation at the immunoglobulin heavy-chain locus of a mouse myeloma cell line

The spontaneous mutation rate of immunoglobulin genes expressed in myeloma cells is well above that of other genes expressed in these or in other cell types. The nature of such mutations in one myeloma cell line, MPC11, was explored at the molecular level. Included in this study were MPC11 variants representing 24 independent and spontaneous mutations affecting immunoglobulin secretion. Of the mutants studied, 19 had ceased immunoglobulin heavy chain (IgH) production (nonproducers), and 5 produced from as little as 1/1,000 to as much as 1/10 the amount of immunoglobulin produced by MPC11 (low producers). Only one of the MPC11 mutants (a nonproducer) showed no evidence of DNA rearrangement in or near the expressed IgH gene. The formerly expressed gamma 2b gene had been deleted in 18 of the 19 nonproducers. All of the low producers had undergone DNA rearrangement in or near the expressed IgH gene, and three of them produced immunoglobulin of a new heavy chain class. The cause for reduced heavy-chain synthesis in the low producers is not yet known. However, in several of these mutants, the defect appeared to be posttranscriptional. In these cell lines, steady-state IgH mRNA levels were much lower than in the parent cell line, while the heavy-chain gene transcription rate remained unchanged.

RNA sequence containing hexanucleotide AAUAAA directs efficient mRNA polyadenylation in vitro

To determine whether a specific nucleotide sequence is required to direct polyadenylation of a simian virus 40 early pre-mRNA in a soluble HeLa whole-cell lysate, we constructed a series of rearranged and deleted DNA templates, transcribed them in vitro, and determined whether the resultant RNAs could be polyadenylated when incubated in whole-cell lysate. When a 237-base-pair DNA fragment encoding the 3' end of the simian virus 40 early pre-mRNA was transferred to recombinant plasmids encoding RNAs that were not substrates for polyadenylation, the resultant RNAs could now be polyadenylated efficiently. In one case, the chimeric RNA was polyadenylated even more efficiently than was the original simian virus 40 early transcript. Analysis of the RNAs produced from the deletion mutant templates revealed that only RNAs containing at least one copy of the AAUAAA sequence situated near the 3' end and implicated in 3'-end formation and polyadenylation in vivo could be polyadenylated in vitro. Surprisingly, this sequence directed polyadenylation of pre-mRNAs not only when near the RNA 3' end, i.e., 50 nucleotides or less away, but also when the 3' end was situated over 400 nucleotides downstream. Thus, our results show that a polyadenylic acid polymerase activity in HeLa lysates can recognize a specific nucleotide sequence in pre-mRNA and then, in the absence of the nucleolytic cleavage that presumably occurs in vivo, locate the RNA 3' end and use it as a primer for polyadenylic acid synthesis.

Fever and proximal tubular function in acute pyelonephritis

The urinary excretion of alpha 1-microglobulin (alpha 1M), beta 2-microglobulin (beta 2M), retinol-binding protein (RBP) and N-acetyl-beta-D-glucosaminidase (NAG) as markers of proximal tubular dysfunction was measured in various forms of urinary tract infections (UTI) and in fever due to non-renal infections. The urinary concentration of these proteins was significantly increased in acute pyelonephritis compared with acute cystitis and asymptomatic bacteriuria. Tubular proteinuria and enzymuria could also be demonstrated in subjects with fever of non-renal origin and corresponded to the findings of pyelonephritis. It is suggested that fever per se is the most likely cause of the tubular proteinuria seen in acute pyelonephritis. In localizing an acute UTI characterization of the urinary protein profile seems to have no advantage over a carefully measured body temperature. The urinary excretion of alpha 1M,beta 2M and RBP were highly correlated, while urinary NAG activity was less correlated to these low-molecular weight proteins. Fibrin degradation product D (FDP-D) was detected in the urines in 60% of the patients with acute pyelonephritis and in one third of those with acute cystitis. The estimation of FDP in urine therefore seems to be of little value in the level diagnosis of UTI.

Black thyroid: clinical manifestations, ultrastructural findings, and possible mechanisms

Ultrastructural examination of three black thyroid glands showed lysosomal accumulations of lipofuscin-like pigment and granular electron-dense material in association with 1) a minocycline-associated black thyroid with normal thyroid function; 2) a minocycline-associated black thyroid with a significant inflammatory component, fibrosis, and primary hypothyroidism; and 3) a black thyroid gland with no exposure to minocycline. The deposition of the pigments in the three cases resulted in macroscopically recognizable black thyroid glands. It is speculated that an imbalance in lysosomal function accounts for this abnormality. The glandular hypofunction documented in case 2 is unique and confirms the need to monitor function carefully in patients who are receiving minocycline. In one case electrondense deposits were identified in the thyroid gland interstitium.

Cluster analysis of chromatographic profiles of urine proteins

A method to examine and classify the chromatograms of urinary proteins, separated on a fast protein liquid chromatography system, is presented. For the analyses a measure of similarity between chromatogram profiles is defined and this is used to implement a statistical cluster analysis technique for the identification of a system of classification. The resulting classification can be related to a clinical assessment of the proteinuria of the sample urines, which are from patients with various renal disorders.

Renal proximal dysfunction in patients with rheumatic diseases

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Osmotic deformation of red blood cell ghosts induced by carbohydrates

The osmotic response of bovine red blood cell ghosts to a series of sugars is studied by light scattering. The sealed and right-side-out ghosts are prepared by the procedure of Steck and Kant (Steck, T.L. and Kant, J.A. (1974) Methods Enzymol. 31, 172-180), swollen in a hypotonic phosphate-buffered saline solution and their size and shape determined by elastic and quasielastic light scattering. Different carbohydrates are then added to the suspending medium in order to examine the osmotic responses, and the osmotic deformation of ghosts is shown to be spherically symmetric. Having thus established the deformation behavior, we then rank the osmotic activity of a carbohydrate relative to a standard, i.e., raffinose. It is found that the osmotic response of the ghosts to sucrose is about the same as that to raffinose, and the response to the smaller carbohydrates simply follows the number of carbons in various sugars; glucose and fractose are about 1.7 times less effective than raffinose, and pentaerythritol and meso-erythritol are 2.3 times less effective. Glyceraldehyde, which is 3.6 times less effective than raffinose, is the least effective sugar analog among those that we have tested.

Urinary protein profiles after burn injury

A study of the change of urinary protein excretion has been made in 26 patients followed from the time of admission to time of discharge from the Yorkshire Regional Burn Centre (7-200 days). Total protein, IgG and albumin (as indicators of glomerular function) and alpha 1-microglobulin, beta 2-microglobulin, retinol binding protein and N-acetyl-beta-D-glucosaminidase (as indicators of proximal tubular function) as well as the patterns on SDS polyacrylamide gel electrophoresis were examined. Patients were divided into three groups according to their urinary protein profiles. The first group was 3 patients who showed little or no evidence of proteinuria; the second group consisted of 7 patients who showed a mild and transient tubular proteinuria, all of whom recovered normal function within one week. The third group, 16 patients, developed moderate to severe proteinuria usually started as a mixed pattern of glomerular and tubular proteinuria, characterized by the excretion of a high level of total protein. After a few days, this pattern changed to a typical tubular proteinuria and the latter could last for as long as 200 days; in some of these patients a secondary increase of low molecular weight protein excretion occurred either due to a latent renal complication or induced by the administration of aminoglycosides. There is a close correlation between the intensity and patterns of the proteinuria and the severity and clinical progress of the burn.

Alpha-1-microglobulin: an indicator protein for renal tubular function

A comparison of urinary alpha 1-microglobulin concentrations to the behaviour of other indicators of renal tubular disorders, beta 2-microglobulin, retinol-binding protein and N-acetyl-beta-D-glucosaminidase (NAG) has been made. In acute tubular disorders the concentrations of urinary beta 2M and RBP are highly correlated (r = 0.89) but this is less marked for alpha 1M and beta 2M (r = 0.55) and alpha 1M and RBP r = 0.48. NAG tends to run a parallel course to alpha 1M concentrations but lags behind the recovery of low molecular weight protein reabsorption following injury of the tubular cells. The concentrations of alpha 1M, and in particular its stability at low pH suggest that this protein may be useful in screening for tubular abnormalities and detecting chronic asymptomatic renal tubular dysfunction. Urinary alpha 1M greater than 15 mg/g creatinine is strongly suspicious of a proximal tubular dysfunction. The distinction between pure tubular proteinuria and mixed glomerular and tubular proteinuria requires further analysis.

Aggregation equilibria of Escherichia coli RNA polymerase: evidence for anion-linked conformational transitions in the protomers of core and holoenzyme

The aggregation equilibria of Escherichia coli RNA polymerase core and holoenzyme have been studied by velocity sedimentation as a function of [NaCl] both in the presence and in the absence of MgCl2. Effects of other anions (F- and I-), pH, and temperature have also been examined. Diffusion coefficients obtained by quasi-elastic light scattering (QLS) at high and low salt concentrations were used in conjunction with sedimentation coefficients under these conditions to obtain molecular weights of the protomer and aggregates of the core enzyme. At low salt concentration, core aggregates to a tetramer in the absence of MgCl2 and to an octamer in the presence of MgCl2. Some ambiguity exists in the interpretation of the sedimentation and QLS data for holoenzyme. The sedimentation results are consistent with the formation of dimers at low salt, both in the presence and in the absence of MgCl2. In all cases, equilibrium constants were calculated assuming a simple monomer--j-mer stoichiometry. These equilibrium constants are extremely sensitive functions of the concentration and type of monovalent anion. In Cl-, aggregation of both core and holoenzyme begins abruptly when the salt concentration is reduced below approximately 0.2 M (at a protein concentration of approximately 0.30 mg/mL); for core, substitution of I- for Cl- suppresses aggregation while F- enhances aggregation at a fixed anion concentration. No specific effect of monovalent cations (Na+, NH4+) is observed; Mg2+ has no effect on holoenzyme dimerization and has little effect on the salt range of core aggregation, though the stoichiometries of the core aggregates in the presence and absence of Mg2+ differ. Anion effects on these equilibria were modeled by assuming that a class of anion-binding sites on the protomer is not present in the aggregate, so that anion release accompanies aggregation. Analytical expressions for several models of the effect of anions on the aggregation equilibria were derived by using the method of binding polynomials. The salt dependence of the aggregation equilibria in the absence of Mg2+ appears inconsistent with a model in which the anion-binding sites on the protomer are independent (noncooperative), but it is well described by a model in which anion binding to the protomers occurs in a completely cooperative manner. The molecular basis of this apparent cooperative effect of anions on the aggregation equilibria is proposed to be an allosteric effect of anions on conformational equilibria of the protomers of core polymerase and the holoenzyme. Implications of such a salt-dependent conformational transition for the DNA-binding interactions of the enzyme are considered.

Electric and optical anisotropy and their osmotically induced changes of photoreceptor disk membrane vesicles

Electro-optical characterization of the photoreceptor disk membrane vesicle is performed by examining the electric field and concentration dependence of the study-state birefringence of aqueous suspensions of the vesicles. The electric polarizability anisotropy is found to be negative and of large magnitude: alpha 1 - alpha 2 = -(1-3) X 10 cm3. The optical anisotropy is determined to be also negative but of small magnitude: g 1 - g 2 = -1 X 10(-7). The specific Kerr constant deduced from the concentration dependence of the Kerr constant is found to be very large: Ksp = 7 X 10(-4) e.s.u. Upon deforming the vesicles osmotically from the spherical shell to the disk structure, the steady-state birefringence increases by an order of magnitude which is attributed solely to the increase in optical anisotropy attending the corresponding change in the geometric eccentricity of the vesicle. A plausible birefringence mechanism based on the known structural features of the vesicles is proposed, which would account for these findings.

Lateral diffusion of photopigments in photoreceptor disk membrane vesicles by the dynamic Kerr effect

The lateral diffusion of photopigment molecules in the photoreceptor disk membranes, osmotically swollen into spherical vesicles, has been investigated by dynamic Kerr effect measurements. Upon application of a rapidly reversing bipolar electric field to dilute aqueous suspensions of bovine disk membrane vesicles, the birefringence transient shows a characteristic rise and a deep dip corresponding to the first and second pulses, respectively. The birefringence transient is ascribed to the slowly induced dipole moment caused by electric field induced displacement of the photopigment distribution on the vesicular surface. The lateral translational diffusion coefficient is estimated from the time constant of the slowly induced dipole as D = (3.3 +/- 1.2) X 10(-9) cm2 s-1. When spermine, a cationic tetraamine, is bound to the disk membrane vesicles, the relaxation time of the slowly induced dipole is shown to become longer, indicating that the birefringence mechanism is indeed due to the field-induced photopigment displacement.

Permeability to ions of bovine retinal disk membrane vesicles in the bleached state

The permeability of the bleached disk membrane of retinal rod outer segments to univalent and divalent ions is studied by light scattering. The membranes are isolated from frozen dark-adapted bovine retinae, swollen into spherical vesicles in a hypotonic medium and bleached in dilute suspension and their size is determined by elastic and quasi-elastic light scatterings. Various electrolytes are then added to the suspending medium in order to examine their osmotic activity relative to the vesicles deformation characteristics. By following the deformation behavior of the membrane vesicles by elastic light scattering in terms of the oblate ellipsoidal shell model, the osmotic activity of a given electrolyte is qualitatively deduced and thereby the permeability of the membrane to the electrolyte is ranked in reference to a chosen standard, i.e., sucrose. By this method, we show that the permeabilities to Na+, K+, Mg2+ and Ca2+ are all alike, and those to halides (F-, Cl-, Br-, I-), nitrate and phosphates (HPO4(2-)/H2PO4-) are similar. Acetate, however, is about 3-times more permeative, while sulfate is less permeative than the other anions by about the same factor. The viability of our method is checked with use of an ionophore, lasolocid (X-537A), by establishing partial recovery from the osmotic deformation through the suppression of the cation osmotic effect. Ion-induced aggregation and pH-dependent size and shape changes are both found to be insignificant.

Dynamic kerr effect measurements on photoreceptor disk membrane vesicles

Dynamic Kerr effect measurements were performed with dilute aqueous suspensions of monodisperse spherical vesicles (approximately 1 micron diameter), isolated from the rod outer segment of bovine retina. A large birefringence, amounting to the specific Kerr constant of 10(-3) esu, can be observed. When a sufficiently long duration pulse (1 s) is applied, the decay of birefringence can be represented by a single exponential profile, yielding a relaxation time of 100 +/- 20 ms in 1 mM imidazole buffer. This is consistent with the rotatory relaxation time of these spherical membrane vesicles. When a short duration is applied, the birefringence increases more steeply and the decay profile contains several components. The slowest (terminal) relaxation time is 86 +/- 15 ms is due to the same process as the one observed in the slow pulse case.