Selective Defluorination of Trifluoromethyl Substituents by Conformationally Induced Remote Substitution

The selective reduction of an aromatic trifluoromethyl substituent to a difluoromethyl substituent may be achieved by base-promoted elimination to form a difluoro-p-quinomethide which is trapped by an intramolecular nucleophile. High yields are obtained when the nucleophilic trap entails the conformationally favoured cyclisation of an aminoisobutyric acid (Aib) derivative. The resulting cyclised difluoromethyl-substituted arylimidazolidinone products are readily converted to versatile difluoromethyl-substituted aldehydes by reduction and hydrolysis. Defluorination is successful on a range of benzenoid (both para and ortho CF3-substituted) and heterocyclic substrates. Double defluorination may likewise be achieved sequentially, or in a single step, from an Aib dipeptide derivative.

Variation in pollinator visitation among garden cultivars of marigold, portulaca, and bidens

Due to declines in pollinator populations, many people are now interested in learning about which annual flowers they can plant in their garden to better support pollinators. However, reports of experimental evaluation of cultivars of annual flowers for attraction to pollinators are scarce. We sampled pollinators visiting six cultivars of marigold (Tagetes erecta and T. patula), ten cultivars of bidens (Bidens ferulifolia and B. aurea), and eight cultivars of portulaca (Portulaca oleracea and P. grandiflora) for two years to compare pollinator visitation rates among cultivars within each flower type. Pollinators collected on flowers in research plots were categorized into four groups, honey bees (Apis mellifera), common eastern bumble bees (Bombus impatiens), wild bees, and syrphids, to show the proportion of different pollinator visitors to each cultivar. Pollinator visitation rates varied significantly among cultivars of marigold, bidens, and portulaca, with some cultivars having as much as 10-fold the visitation rate of other cultivars of the same flower type. In the second year we also evaluated nectar production and nectar quality of the most and least visited cultivars of portulaca and bidens. Our results show that pollinators have a strong preference for cultivars that produce the most nectar or nectar with the highest sugar content. This research will better inform entomologists, growers, educators, and plant breeders, about which cultivars of marigold, portulaca, and bidens are visited the most by pollinators, and how to accurately determine this at the cultivar level.

Complex interactions between nicotine and resveratrol in the Drosophila melanogaster wing spot test

Nicotine (NIC) and resveratrol (RES) are chemicals in tobacco and wine, respectively, that are widely consumed concurrently worldwide. NIC is an alkaloid known to be toxic, addictive and to produce oxidative stress, while RES is thought of as an antioxidant with putative health benefits. Oxidative stress can induce genotoxic damage, yet few studies have examined whether NIC is genotoxic in vivo. In vitro studies have shown that RES can ameliorate deleterious effects of NIC. However, RES has been reported to have both antioxidant and pro-oxidant effects, and an in vivo study reported that 0.011 mM RES was genotoxic. We used the Drosophila melanogaster wing spot test to determine whether NIC and RES, first individually and then in combination, were genotoxic and/or altered the cell division. We hypothesized that RES would modulate NIC’s effects. NIC was genotoxic in the standard (ST) cross in a concentration-independent manner, but not genotoxic in the high bioactivation (HB) cross. RES was not genotoxic in either the ST or HB cross at the concentrations tested. We discovered a complex interaction between NIC and RES. Depending on concentration, RES was protective of NIC’s genotoxic damage, RES had no interaction with NIC, or RES had an additive or synergistic effect, increasing NIC’s genotoxic damage. Most NIC, RES, and NIC/RES combinations tested altered the cell division in the ST and HB crosses. Because we used the ST and HB crosses, we demonstrated that genotoxicity and cell division alterations were modulated by the xenobiotic metabolism. These results provide evidence of NIC’s genotoxicity in vivo at specific concentrations. Moreover, NIC’s genotoxicity can be modulated by its interaction with RES in a complex manner, in which their interaction can lead to either increasing NIC’s damage or protecting against it.

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Nicotine was genotoxic at specific concentrations in the Drosophila wing spot test.

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Resveratrol protected against nicotine’s genotoxic effects at some concentrations.

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Resveratrol increased nicotine’s genotoxicity at specific concentrations.

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Nicotine and resveratrol have a complex interaction in vivo.

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Studying chemicals in combination in vivo may uncover unexpected interactions.

Triarylmethanes and their Medium-Ring Analogues by Unactivated Truce-Smiles Rearrangement of Benzanilides

Intramolecular nucleophilic aromatic substitution (Truce–Smiles rearrangement) of the anions of 2‐benzyl benzanilides leads to triarylmethanes in an operationally simple manner. The reaction succeeds even without electronic activation of the ring that plays the role of electrophile in the S_NAr reaction, being accelerated instead by the preferred conformation imposed by the tertiary amide tether. The amide substituent of the product may be removed or transformed into alternative functional groups. A ring‐expanding variant (n to n+4) of the reaction provided a route to doubly benzo‐fused medium ring lactams of 10 or 11 members. Hammett analysis returned a ρ value consistent with the operation of a partially concerted reaction mechanism.

The logistical management of tertiary urethral disease in the United Kingdom: Implications from an online audit of male reconstructive urethral surgery

Objective:

To determine those patient groupings, based on volume and risk, whose optimal urethral reconstructive management might be provided by a reorganisation of UK reconstructive surgeons.

Methods:

Between 2010 and 2017, ~689 men/year were enrolled onto an online audit platform collecting data about urethral reconstruction in the UK; this accrual was compared against hospital episode statistics (HES). The available workforce, and where this was based, was collected. Individual and institutional incumbent patient volumes, pathology, surgical complexity and outcomes from treatment were collated to stratify volume/risk groups.

Results:

More than 90% of all HES-recorded data were accrued, being provided by 50 surgeons at 39 operative sites. Most reconstructive surgery was provided at 10 centres performing >20 procedures/year. More than 50% of all interventions were of a high-volume low-risk type. Of activity, 32.3% was intermediate volume or moderate risk, and 12.5% of men presented for lower-volume or higher-risk procedures.

Conclusion:

Correlation of detailed volume/outcome data allows the definition of patient populations presenting for urethral reconstruction. Stratification of each group’s management, to optimise the surgical outcome, may be applied to a hierarchical service delivery model based on the complexity of the patient’s presenting urethral pathology.

Level of evidence:

Level IV

Nanoscale mapping of quasiparticle band alignment

Control of atomic-scale interfaces between materials with distinct electronic structures is crucial for the design and fabrication of most electronic devices. In the case of two-dimensional materials, disparate electronic structures can be realized even within a single uniform sheet, merely by locally applying different vertical gate voltages. Here, we utilize the inherently nano-structured single layer and bilayer graphene on silicon carbide to investigate lateral electronic structure variations in an adjacent single layer of tungsten disulfide (WS₂). The electronic band alignments are mapped in energy and momentum space using angle-resolved photoemission with a spatial resolution on the order of 500 nm (nanoARPES). We find that the WS₂ band offsets track the work function of the underlying single layer and bilayer graphene, and we relate such changes to observed lateral patterns of exciton and trion luminescence from WS₂.

Sharp atomic interfaces between materials dictate the interface’s electronic properties. The authors use angle-resolved photoemission spectroscopy with a spatial resolution of ~500 nm to investigate the nanoscale electronic band structure and band alignment in a lateral heterostructure composed of WS₂ placed on alternating nano-stripes of monolayer and bilayer graphene.

Skin flap vaginal augmentation helps prevent and cure post obstetric fistula repair urine leakage: a critical anatomical analysis

Our aim was to describe a new surgical method for prophylaxis/cure of post obstetric fistula repair leakage based on restoring vaginal elasticity with Singapore skin flap. The rationale for this operation was based on the integral theory: scarring removes elasticity required for independent function of oppositely acting urethral closure forces so they become 'tethered, forcibly opening the urethra when give the signal to close'. Skin graft restores elasticity and closure. Used prophylactically with Goh type 4 fistula (n = 45), 46% were dry against an expected 19%. In patients with successful fistula closure, still with severe leakage (n = 24), 71% were dry against an expected 26%.

TWEETABLE ABSTRACT

Singapore skin flap restores elasticity and prevents and treats incontinence in patients with successful obstetric fistula repair.

Debrisoft is a wound debridement product, not a wound dressing

In your April 2 edition (News) you highlighted the recent publication of NICE guidance on the Debrisoft monofilament debridement pad, which has the potential to save the NHS about £15 million a year.

Women with obstetric fistula in Ethiopia: a 6-month follow up after surgical treatment

OBJECTIVE

To quantify surgical and quality of life outcomes 6 months after obstetric fistula repair.

DESIGN

A prospective study. Women were examined and questioned at discharge and at follow-up appointment.

SETTING

The Barhirdar Hamlin Fistula Centre, a dedicated unit treating women with obstetric fistula in northern Ethiopia.

POPULATION

All women admitted to the Barhirdar Hamlin Fistula Centre suffering from vesicovaginal (WF) and rectovaginal fistulae (RVF).

METHODS

All women were asked to return for a follow-up appointment 6 months after surgical treatment. A standardised questionnaire and examination were used and information entered into a database.

MAIN OUTCOMES MEASURES

Urinary and anal continence status; extent of return to previous family situation, employment, social activities and reproductive capabilities.

RESULTS

Continence status at discharge was largely maintained at 6 months and quality of life was improved. Many of those incontinent on discharge improved; a small number apparently cured at discharge had later recurrence of incontinence.

CONCLUSIONS

Surgical treatment for obstetric fistula is successful in maintaining continence and improving quality of life of women at 6-months follow up.

The impact of surgical treatment on the mental health of women with obstetric fistula

Obstetric fistula is estimated to affect 2 million women worldwide and has considerable social and psychological effects on affected individuals. In this prospective study, 51 consecutive women with obstetric fistula admitted to the Barhirdar Hamlin Fistula Centre in the north of Ethiopia were screened using the General Health Questionnaire (GHQ-28) for potential mental health disorder before and 2 weeks after fistula surgery. Prior to surgery, all women screened positive. By 2 weeks after, this had dropped to 36% (P = 0.005). 27% of the 45 women who were cured of their incontinence screened positive, while all 6 of those with severe residual incontinence continued to screen positive. We conclude that surgical treatment of obstetric fistula results in marked improvements in mental heath.

Obstetric fistula: Clinical considerations in the creation of a new urethra and the management of a subsequent pregnancy

The paper presents two case studies to illustrate the complexity of repairing obstetric fistula (OF) with neourethral construction when complete circumferential destruction occurred. Using fictitious names, the author describes the personal story and contexts leading to OF development and depression, surgical options, and the prognosis of repair. These cases were documented at the Barhirdar Hamlin Fistula Center in Northern Ethiopia.

Short communication: The circumferential obstetric fistula: characteristics, management and outcomes

Obstetric vesicovaginal fistula is a tragic injury that is widespread in any country where access to emergency obstetric care is limited. More and more people are now interested in treating and caring for these women, but little is known about surgical management, and most operators have developed their own methods through years of experience. One of the more challenging cases to get a functional repair is in those women who have a circumferential defect in the bladder/urethra. This article analyses a series of 77 consecutive circumferential obstetric fistula cases operated in the Barhirdar Hamlin Fistula Centre by the author.

Syphilitic acute posterior placoid chorioretinitis in nonimmuno-compromised patients

PURPOSE

To describe the clinical and angiographic features of three cases of secondary syphilis in immunocompetent patients, which presented as acute posterior placoid chorioretinitis (APPC) to the ophthalmologist.

METHODS

Interventional case series. The aetiology of the APPC was confirmed by serology to be secondary syphilis. Optical coherence tomography, electrophysiology, fundus fluorescein, and indocyanine green (ICG) angiography were performed at presentation and after resolution. Appropriate treatment for secondary syphilis was instituted in each patient.

RESULTS

The clinical features, fundus fluorescein and ICG angiography, multifocal electroretinography (mfERG), and optical coherence tomography findings of APPC are described. All three patients had a satisfactory resolution of the APPC with improvement in visual acuity.

CONCLUSIONS

APPC in secondary syphilis can occur even in immunocompetent patients. A high index of suspicion is required for early diagnosis of this condition resulting in a good visual outcome with adequate treatment. mfERG and optical coherence tomography are useful in the diagnosis and follow-up of these patients.

Effect of age related macular degeneration on the Eger macular stressometer photostress recovery time

AIM

To assess the repeatability of Eger macular stressometer (EMS) measures of photostress recovery and determine their association with other measures of visual function.

METHODS

EMS photostress recovery time was measured in 90 patients with bilateral exudative age related macular degeneration (AMD), 19 with bilateral atrophic AMD and 47 with both forms of the condition (mean age 79 (SD 13) years). Measurements were made on two occasions separated by 1 year. Intrasession repeatability was assessed by repeating the measures after a 10 minute recovery period at the first visit. Distance visual acuity was measured with a logMAR chart, near visual acuity with a MNRead chart at 25 cm, contrast sensitivity with a Pelli-Robson chart, and the presence of central visual disturbance assessed with an Amsler grid. A questionnaire was used to assess self reported difficulties with glare recovery.

RESULTS

The average EMS recovery time was 11.0 (SD 8.9) seconds, decreasing by 1.6 (5.2) seconds on repeated measurement (p<0.05). EMS photostress recovery was not correlated with visual function measures or subjective difficulties with lights (p>0.05). EMS photostress recovery time did not predict those whose vision decreased over the following year compared with those among whom it remained stable.

CONCLUSIONS

The EMS test is not a useful tool in determining the severity or progression of AMD.

A new technique for the surgical management of urinary incontinence after obstetric fistula repair

Obstetric vesicovaginal fistula is a debilitating injury still occurring widely throughout the developing world. Fortunately, now more and more surgeons are becoming aware of this previously hidden problem, and many thousands of women are receiving treatment each year. What is difficult for the fistula surgeon are those women, who after having their vesicovaginal fistula successfully closed, return to their doctor, still just as incontinent as they were with the fistula still open. This study describes a new, simple and cheap surgical procedure that promises to improve the lot of these unfortunate women.

Lack of value of the Martius fibrofatty graft in obstetric fistula repair

OBJECTIVE

To ascertain if the Martius graft is of benefit to successful surgical outcome in obstetric fistula repair.

METHOD

A retrospective analysis of 440 consecutive obstetric fistula repairs performed by the author in the Addis Ababa Fistula Hospital, Ethiopia or the Barhirdar Hamlin Fistula Center, Ethiopia, with or without the Martius fibrofatty graft. These were further divided into 13 subgroups of vesicovaginal fistula and all groups compared against two outcomes; fistula closure and presence of residual urethral incontinence following repair. Results were statistically analyzed with the Fisher's exact or Chi-squared test.

RESULTS

There was no statistical difference between groups with regards to breakdown of repair but a higher rate of residual incontinence in 3 subgroups with the Martius graft.

CONCLUSION

The Martius graft can be safely omitted from obstetric fistula repair if the surgeon is experienced, and performs the same type of repair as used in this analysis.

Risk factors for developing residual urinary incontinence after obstetric fistula repair

Obstetric vesicovaginal fistula is a devastating cause of urinary incontinence worldwide. More attention is being focused on treating these patients by various philanthropic societies but very little is known about the complications of surgery. One of the most common complications is that the woman is left with residual urinary incontinence despite the defect being successfully closed. If risk factors for this could be identified, then perhaps more appropriate surgical techniques could be developed with the aim of remedying the incontinence.

Proposal for a tiered approach to developmental toxicity testing for veterinary pharmaceutical products for food-producing animals

In order to establish the safety of veterinary drug residues in human food, a number of toxicological evaluations are required, including the assessment of potential risks to development. In the light of the use of developmental toxicity testing for risk characterization, we evaluated whether conducting these tests in more than one species was redundant. Review of the published Summary Reports of recommendations of the EU Committee for Veterinary Medicinal Products supplemented with data from the Joint FAO/WHO Expert Committee on Food Additives (JECFA) reports on veterinary drug residues in food identified 120 compounds, of which 105 had teratogenicity information in more than one species. The analysis of these compounds, representing a variety of chemical and pharmacological classes, provided justification for consideration of the use of a tiered approach for developmental toxicity evaluation of veterinary drugs for food-producing animals. The tiered approach begins with developmental toxicity testing in a rodent species, preferably the rat. If teratogenicity is observed, no testing in a second species would be required, except under specific circumstances where the ADI is determined based on the NOEL from this study. If a negative or an equivocal result for teratogenicity were observed in the rodent, then a developmental test in a second species, preferably the rabbit, would be conducted. The tiered approach provides thorough hazard identification, based on the use of a second species for compounds negative for teratogenicity in the rodent, and maintains maximum public protection based on the extremely low potential for human exposure to these compounds, while making a genuine attempt to limit unnecessary animal testing.

The effects of hypergravity and substrate vibration on vestibular function in developing chickens

We used linear vestibular evoked potentials (VsEPs) to characterize peripheral and central vestibular function in birds following embryogenesis at 2G centrifugation or at elevated levels of vibration (+20dB re: background levels). Additionally, we characterized peripheral and central vestibular adaptation to 2G centrifugation in early post-hatch birds. Linear VsEP response peak latencies, amplitudes, thresholds and input/output functions were quantified and compared between experimental and control animals. Birds vibrated throughout embryogenesis and up to one-week post-hatch revealed no changes in linear VsEP response components compared to control siblings. Birds centrifuged at 2G throughout embryogenesis also evidenced no changes in the linear VsEP measured at hatch (P0). Significant changes were seen, however, for linear VsEPs of post-hatch birds placed at 2G for 7 days beginning on post-hatch day 5. Linear VsEPs for these animals displayed significant reductions in response amplitudes associated with peaks P2, N2 and P3, response peaks generated by central neural relays of gravity receptors. The earliest response components, generated by the peripheral vestibular nerve (i.e., P1, N1), were not significantly altered with the 7-day exposure to 2G. Thus, there was no evidence of generalized changes in peripheral gravity receptor excitability or in the rate of maturation in developing animals under increased levels of gravity or vibration. If gravity level plays a critical role in shaping peripheral vestibular ontogeny at magnitudes between 1 and 2G, then it may serve to stabilize function under changing G-fields or it may operate on physiological features that can not be resolved by the VsEP. In contrast, exposure to elevated gravity during post-hatch periods does alter central vestibular function thus providing direct evidence for central vestibular adaptation to the gravitational environment. The fact that central functional change was observed in hatchlings and not embryos, raises the possibility that the first 2-weeks post-hatch may be a critical period of "heightened developmental sensitivity" to hypergravity.

The representation of pleasant touch in the brain and its relationship with taste and olfactory areas

Although there has been much investigation of brain pathways involved in pain, little is known about the brain mechanisms involved in processing somatosensory stimuli which feel pleasant. Employing fMRI it was shown that pleasant touch to the hand with velvet produced stronger activation of the orbitofrontal cortex than affectively neutral touch of the hand with wood. In contrast, the affectively neutral but more intense touch produced more activation of the primary somatosensory cortex than the pleasant stimulus. This indicates that part of the orbitofrontal cortex is concerned with representing the positively affective aspects of somatosensory stimuli, and in further experiments it was shown that this orbitofrontal area is different from that activated by taste and smell. The finding that three different primary or unlearned types of reinforcer (touch, taste, and smell) are represented in the orbitofrontal cortex helps to provide a firm foundation for understanding the neural basis of emotions, which can be understood in terms of states elicited by stimuli which are rewarding or punishing.

The neurophysiology of taste and olfaction in primates, and umami flavor

To investigate the neural encoding of glutamate (umami) taste in the primate, recordings were made from taste responsive neurons in the cortical taste areas in macaques. Most of the neurons were in the orbitofrontal cortex (secondary) taste area. First, it was shown that there is a representation of the taste of glutamate which is separate from the representation of the other prototypical tastants sweet (glucose), salt (NaCl), bitter (quinine) and sour (HCl). Second, it was shown that single neurons that had their best responses to sodium glutamate also had good responses to glutamic acid. Third, it was shown that the responses of these neurons to the nucleotide umami tastant inosine 5'-monophosphate were more correlated with their responses to monosodium glutamate than to any prototypical tastant. Fourth, concentration response curves showed that concentrations of monosodium glutamate as low as 0.001 M were just above threshold for some of these neurons. Fifth, some neurons in the orbitofrontal region, which responded to monosodium glutamate and other food tastes, decreased their responses after feeding with monosodium glutamate to behavioral satiety, revealing a mechanism of satiety. In some cases this reduction was sensory-specific. Sixth, it was shown in psychophysical experiments in humans that the flavor of umami is strongest with a combination of corresponding taste and olfactory stimuli (e.g., monosodium glutamate and garlic odor). The hypothesis is proposed that part of the way in which glutamate works as a flavor enhancer is by acting in combination with corresponding food odors. The appropriate associations between the odor and the glutamate taste may be learned at least in part by olfactory to taste association learning in the primate orbitofrontal cortex.

The study of thermal and gross morphologic properties of polyglycolic acid upon annealing and degradation treatments

The objective of this study is to alter the fiber morphology of a linear aliphatic polyester, polyglycolic acid, by annealing treatment and to examine the changes of its degradation properties. The annealing was done at 150 degrees C, 170 degrees C, and 190 degrees C, and the specimens were annealed in four different strained conditions, freely hung, 0, 1, and 10%. After annealing treatments, the specimens were subject to in vitro hydrolytic degradation by immersing them in phosphate-buffer solution of pH 7.4 at 37 degrees C for up to 28 days. The thermal properties and gross morphology of the specimens were obtained. It was found that annealing treatments resulted in initial higher levels of crystallinity, which, in turn, influenced the hydrolytic degradation of the fiber. Among all the annealing conditions, the freely hung specimens annealed at 190 degrees C exhibited the most pronounced annealing effect on hydrolytic degradation, and was consistent with the observed gross morphologic changes. The change in the characteristics of fiber structure (i.e., the return to the stage of less oriented conformation upon freely hung annealing) was thought to be the cause.

The effect of annealing treatments on the tensile properties and hydrolytic degradative properties of polyglycolic acid sutures

The purpose of this research was to examine the effect of annealing treatments on the mechanical properties of polyglycolic acid sutures, and their subsequent influence on PGA degradation properties. An attempt was made to develop a better understanding of the degradation mechanism of synthetic absorbable sutures, including the relationship of their structure, morphology, and mechanical properties. PGA sutures were annealed under selected axial strain (freely hung, 0%, 1%, 10%), at four temperatures (150 degrees C, 170 degrees C, 180 degrees C, 190 degrees C), and two times (5 and 20 min). The annealed PGA specimens were then subjected to hydrolysis in phosphate-buffer solutions (pH = 7.4) for up to 28 days at 37 degrees C. Tensile properties were used to evaluate the effect of annealing treatments. The data were subjected to statistical analysis using the SAS system. All of the one-, and many of the two- and three-factor interactions were found to be statistically significant. Annealing treatments did alter the mechanical properties of PGA sutures, as well as their degradation properties. Except for the increase in tenacity of samples with increasing percent extension, all other respects of the annealing treatments resulted in lower tenacity and breaking elongation when compared with the control samples. Sutures that have been exposed to any level of axial tension during annealing, however, exhibited a lower rate of hydrolytic degradation than the freely hung suture samples. The reduction of the characteristics of fiber structure due to the tendency of the tie-chain molecules to acquire the less constrained conformations and thus to bring the crystal blocks they connect back to the original arrangement before drawing is believed to be responsible for the freely hung specimens to behave quite differently from the clamped and stressed PGA samples.

Failure of lactoperoxidase to iodinate specifically the plasma membrane of cucurbita tissue segments

An attempt has been made to use lactoperoxidase-catalyzed iodination of excised Cucurbita hypocotyl hooks to monitor the distribution of plasma membrane fragments relative to that of phytochrome in particulate fractions from this tissue. Upon fractionation, the iodinated tissue yields a 20,000g pellet which contains 58% of the trichloroacetic acid-precipitable (125)I at a specific radioactivity 12 times that of the proteins in the supernatant. On sucrose gradients, the labeled fraction has a mean isopycnic density of 1.15 g . cm(-3). The distribution profile is distinct from that of the total particulate protein and does not coincide with either mitochondrial or endoplasmic reticulum markers. These observations satisfy operational criteria commonly accepted in other systems as indices of selective labeling of the cell surface. The sucrose gradient profiles of the phytochrome and (125)I in the 20,000g pellets are noncoincident. In the absence of more direct evidence, this is readily interpreted to indicate a lack of association of the pigment with the plasma membrane.Autoradiographic analysis indicates, however, that the (125)I is almost exclusively associated with an amorphous film (possibly phloem-exudate protein) overlying the cut cells at the point of prelabeling excision and along the outer physical surface of the hypocotyl cuticle. No evidence of plasma membrane labeling is apparent. The observed membrane-like behavior of the iodinated material upon cell fractionation is attributed to the preferential posthomogenization association of this material with a particular membrane fraction(s). These data indicate that in addition to the well recognized potential for spurious labeling of the internal cytoplasmic proteins of leaky cells, a further source of ambiguity in surface-labeling experiments should be considered. That is, the potential for labeling extracellular proteins of nonplasma membrane origin but with a capacity to become associated with membranes upon homogenization.