Evaluation of contemporary olanzapine- and netupitant/palonosetron-containing antiemetic regimens for chemotherapy-induced nausea and vomiting

INTRODUCTION

This post-hoc analysis retrospectively assessed data from two recent studies of antiemetic regimens for chemotherapy-induced nausea and vomiting (CINV). The primary objective was to compare olanzapine-based versus netupitant/palonosetron (NEPA)-based regimens in terms of controlling CINV during cycle 1 of doxorubicin/cyclophosphamide (AC) chemotherapy; secondary objectives were to assess quality of life (QOL) and emesis outcomes over four cycles of AC.

METHODS

This study included 120 Chinese patients with early-stage breast cancer who were receiving AC; 60 patients received the olanzapine-based antiemetic regimen, whereas 60 patients received the NEPA-based antiemetic regimen. The olanzapine-based regimen comprised aprepitant, ondansetron, dexamethasone, and olanzapine; the NEPA-based regimen comprised NEPA and dexamethasone. Patient outcomes were compared in terms of emesis control and QOL.

RESULTS

During cycle 1 of AC, the olanzapine group exhibited a higher rate of 'no use of rescue therapy' in the acute phase (olanzapine vs NEPA: 96.7% vs 85.0%, P=0.0225). No parameters differed between groups in the delayed phase. The olanzapine group had significantly higher rates of 'no use of rescue therapy' (91.7% vs 76.7%, P=0.0244) and 'no significant nausea' (91.7% vs 78.3%, P=0.0408) in the overall phase. There were no differences in QOL between groups. Multiple cycle assessment revealed that the NEPA group had higher rates of total control in the acute phase (cycles 2 and 4) and the overall phase (cycles 3 and 4).

CONCLUSION

These results do not conclusively support the superiority of either regimen for patients with breast cancer who are receiving AC.

Assessing the use of a smartphone app to teach eye screening to opticians

INTRODUCTION

Torch-light Eye Screening Test (TEST) is a simple eye screening technique designed for use by opticians to look for common anterior segment eye conditions. The TEACHES-Learning Electronic Module (TEACHES-LEM) is an e-learning platform that was developed to teach opticians to perform TEST. The objective of this study was to compare the effectiveness of TEACHES-LEM with face-to-face training (F2FT) in the training and assessment of knowledge among opticians.

METHODS

Participants were randomly assigned in this experimental study to receive either the intervention group ((TEACHES-LEM, n = 60) or the control group (F2FT, n = 57). The conceptual knowledge of TEST was assessed with a 20-item clinical scenario-based multiple choice question (MCQ) test before and after teaching (immediately post-teaching and 1-month post-teaching). The MCQ test was developed by three ophthalmologists to give face validity.

RESULTS

The pre-teaching test scores (TS), indicating prior knowledge, were comparable in both groups (10.02 ± 2.79 versus 10.40 ± 4.17, p = 0.563, independent t test). The mean immediate post teaching score for TEACHES-LEM was 13.3 ± 4.01 versus 12.3 ± 3.29 in the F2FT group (p = 0.170, independent t test). The mean post 1-month teaching score for TEACHES-LEM and F2FT groups were also comparable, 14.5 ± 4.19 versus 13.4 ± 3.90 respectively (p = 0.295, independent t test), indicating non-inferiority of TEACHES to F2FT.

CONCLUSION

The TEACHES-LEM e-learning tool is as effective as F2FT in teaching opticians to perform TEST. It is an alternative to face-to-face teaching in delivering knowledge and assessment. The obviation for physical contact will make it a useful teaching tool during the COVID-19 pandemic period.

Medial Rectus Muscle Incarceration in Pediatric Medial Orbital Wall Trapdoor Fractures

PURPOSE

We describe two cases of orbital trapdoor fractures with medial rectus muscle incarceration.

METHODS

Small interventional case series.

RESULTS

This is a retrospective university based report of two healthy males (11 and 14 years old) who developed diplopia following blunt orbital trauma. Both patients had decreased horizontal ocular motility of the involved eye with minimal additional evidence of trauma. Computed tomography (CT) demonstrated no significant bony displacement; however, the left medial rectus muscle was located within the ethmoid sinus in the first and had an abnormal size and shape in the second case. In both cases, during urgent surgical repair, the incarcerated medial rectus muscle was gently released from linear non-displaced medial wall fractures and ocular motility normalized postoperatively.

CONCLUSIONS

In pediatric patients sustaining blunt orbital trauma, medial rectus incarceration should be considered and managed accordingly.

Evaluation of the molecular Xpert Xpress Flu/RSV assay vs. Alere i Influenza A & B assay for rapid detection of influenza viruses

A new FDA-approved Xpert Xpress Flu/RSV assay has been released for rapid influenza virus detection. We collected 134 nasopharyngeal specimens to compare the diagnostic performance of the Xpert assay and the Alere i Influenza A & B assay for influenza A and B virus detection. The Xpert assay demonstrated 100% and 96.3% sensitivity to influenza A and influenza B virus respectively. Its specificity was 100% for both viruses. The Alere i assay demonstrated slightly lower sensitivity but similar specificity to the Xpert Xpress assay. Although the Xpert assay (30 min) required longer processing time than the Alere assay (15 min), the handling procedure of the Alere assay was more complicated than the Xpert assay. As the GenXpert system has higher throughput than the Alere system, it is more suitable for hospital clinical laboratories. Overall, the new Xpert Xpress Flu/RSV assay is a reliable and useful tool for rapid influenza detection.

Traumatic eye injuries due to large unusual foreign bodies: a Singapore case series

PURPOSE

Traumatic eye injuries due to large foreign bodies (FB) are rare. The visual prognosis is often poor in these cases because of severe ocular damage. Staged surgical procedures with eventual enucleation or evisceration are often indicated.

METHODS

Case series.

RESULTS

The authors describe two patients with eye injury due to large FB with visual acuity of no light perception at presentation. Both had initial repair of the ocular injuries and removal of the FB. One patient with an intraocular FB eventually underwent enucleation; the other, with intraorbital FB, had evisceration as a secondary procedure. Orbital implantations were done in both. Neither of the patients had developed sympathetic ophthalmia at the last review.

CONCLUSIONS

The visual outcome of eye injuries due to large FB is poor. Both enucleation and evisceration can be performed with low risk of sympathetic ophthalmia. Prevention remains the best approach to such devastating injuries.

Low-dose intravenous methylprednisolone or conservative treatment in the management of traumatic optic neuropathy

PURPOSE

To compare the efficacy of low-dose intravenous methylprednisolone or conservative treatment in the management of traumatic optic neuropathy.

METHODS

A non-randomized retrospective study of 21 patients (21 eyes) with traumatic optic neuropathy treated between October 95 and November 97 in a tertiary ophthalmology unit. Traumatic optic neuropathy was defined as traumatic visual loss with afferent pupillary defect in the absence of direct injury to the globe or optic nerve. The median follow-up period was one year. Nine patients were treated with 125-250 mg methylprednisolone 6-hourly intravenously for a mean of 3.3 days (range 2-5 days) and 12 patients were treated conservatively. Visual acuity (VA) was measured with a Snellen chart before and after treatment at each follow-up visit. Visual recovery was defined as an improvement of 2 or more Snellen lines one week post-injury or later.

RESULTS

The patients' mean age was 37.1 years (range 12-65 years). There were more males (90.5%) than females (9.5%). Traumatic optic neuropathy was in 12 right eyes and 9 left eyes. The cause of injury included traffic accidents (52.4%), falls (28.6%), assault (14.2%) and others (4.8%). The mean interval between the injury and steroid therapy was 3.6 days (range 1-11 days). Visual recovery was observed in 44.4% of eyes treated with methylprednisolone and in 33.3% treated conservatively (p = 0.673, Fisher's exact test).

CONCLUSIONS

Intravenous methylprednisolone at the dosage and duration used in this retrospective study did not significantly improve the visual recovery of eyes with traumatic optic neuropathy compared to conservative treatment. However, this small sample may not be sensitive enough to detect a small difference in visual recovery rates, and further studies with larger samples may be warranted.

Intraoperative capsular block syndrome masquerading as expulsive hemorrhage

PURPOSE

To describe the clinical features of two cases of intraoperative capsular block syndrome (CBS) mimicking expulsive hemorrhage.

SETTING

The Eye Institute at Tan Tock Seng Hospital, National Healthcare Group, Singapore.

METHODS

Two case reports.

RESULTS

Two patients underwent phacoemulsification under retrobulbar anesthesia and developed severe globe hardening, shallow anterior chamber (AC) and uveal prolapse intraoperatively after hydrodissection. The AC spontaneously deepened in one patient and the operation was converted to extracapsular cataract surgery on suspicion of CBS with posterior capsule rupture, which was confirmed after nucleus expression; anterior vitrectomy was done and an anterior chamber lens implanted. At the eight post-operative month, his best-corrected visual acuity was 6/24 secondary to an epiretinal membrane in the macula. CBS, however, was not recognized in the other patient and caused posterior lens dislocation during attempted phacoemulsification. This patient underwent vitrectomy, removal of the lens nucleus and insertion of a posterior chamber intraocular lens in the sulcus the next day. His best-corrected visual acuity was 6/9 at the tenth postoperative month.

CONCLUSIONS

Intraoperative CBS may mimic expulsive hemorrhage. Early diagnosis of this condition and proper management optimizes the visual outcome.

Lacrimal sac tumour presenting with blood-stained ocular discharge

Malignant epithelial tumours of the lacrimal sac are uncommon. They can mimic chronic dacryocystitis or dacryostenosis to cause a delay in diagnosis. The presence of a medial canthal lump with blood-stained ocular discharge should arouse the suspicion of this diagnosis. The prognosis of lacrimal sac tumour is often guarded especially following tumour recurrence after incomplete resection. We report a patient with squamous cell carcinoma of the lacrimal sac to highlight its presentation and clinical course.

Herpes zoster ophthalmicus and the superior orbital fissure syndrome

Herpes Zoster Ophthalmicus (HZO) is not an uncommon condition in the elderly and the immunocompromised. The common ocular manifestations include blepharoconjunctivitis, keratitis and uveitis. Dramatic presentations like orbital apex syndrome and superior orbital fissure syndromes occur rarely in patients with herpes zoster meningo-encephalitis. We report a patient with herpes zoster meningo-encephalitis and the superior orbital fissure syndrome (SOFS).

A randomized double-masked crossover study comparing latanoprost 0.005% with unoprostone 0.12% in patients with primary open-angle glaucoma and ocular hypertension

PURPOSE

To compare the intraocular pressure)-lowering effect and side effects of latanoprost 0.005% once daily with unoprostone 0.12% twice daily.

METHODS

Sixty patients with primary open-angle glaucoma or ocular hypertension were randomized to receive either latanoprost once daily in the evening and placebo once daily in the morning, or unoprostone twice daily in the morning and evening. The study was double masked and followed a crossover design with two treatment periods of 1 month separated by a 3-week washout period. The intraocular pressure was measured at 9 AM and 5 PM on the baseline and day 28 visits, and at 9 AM on day 2 and day 14 visits of each treatment period. The 9 AM measurement was taken 2 hours and 13 hours after the last drop of unoprostone and latanoprost, and the 5 PM measurement was at 10 and 21 hours, respectively. The mean of the measurements was calculated. Safety parameters were also recorded.

RESULTS

Fifty-six patients completed both treatment periods and had intraocular pressure data available for evaluation. After 1 month of treatment, latanoprost significantly reduced intraocular pressure (mean +/- SEM) by 6.1 +/- 0.5 mm Hg (P <.001) and unoprostone by 4.2 +/- 0.4 mm Hg (P <.001) adjusted from an overall baseline of 22.3 +/- 0.5 mm Hg and 23.2 +/- 0.4 mm Hg, respectively. The difference of 1.9 mm Hg between treatments was statistically significant in favor of latanoprost [P =.003, analysis of covariance (ANCOVA)]. Unadjusted analysis of responders using the percentage decrease in intraocular pressure showed that the proportion of responders in the latanoprost-treated group was greater than in the unoprostone-treated group. Adverse ocular symptoms and findings were mild in both treatment groups. Eye redness and ocular irritation were the most frequently reported events.

CONCLUSIONS

Latanoprost once daily was significantly more effective in reducing intraocular pressure compared with unoprostone twice daily after 1 month of treatment in patients with primary open-angle glaucoma and ocular hypertension. Both drugs were well tolerated with few ocular adverse events.

A novel approach for the fixation of enucleated eyes during microsurgical procedures using common household plumbing accessories

The authors describe a novel approach for the fixation of enucleated eyes during microsurgical procedures using common household plumbing accessories. The device consists of a ring adaptor with 4 round-ended screws placed horizontally at its sides and a plastic hose connector. The enucleated globe is secured in the center of the ring adaptor by gently tightening the screws. The hose connector supports the posterior pole of the globe and is secured onto a styrofoam board that provides a platform for resting the surgeon's hands. The device proved very satisfactory to residents during the teaching of cataract surgery and trabeculectomy on porcine eyes. Our globe fixation device is simple, inexpensive, effective, and readily available. It may be especially useful in developing countries.

Mechanism of transmembrane signaling: insulin binding and the insulin receptor

Transmembrane signaling via receptor tyrosine kinases generally requires oligomerization of receptor monomers, with the formation of ligand-induced dimers or higher multimers of the extracellular domains of the receptors. Such formations are expected to juxtapose the intracellular kinase domains at the correct distances and orientations for transphosphorylation. For receptors of the insulin receptor family that are constitutively dimeric, or those that form noncovalent dimers without ligands, the mechanism must be more complex. For these, the conformation must be changed by the ligand from one that prevents activation to one that is permissive for kinase phosphorylation. How the insulin ligand accomplishes this action has remained a puzzle since the discovery of the insulin receptor over 2 decades ago, primarily because membrane proteins in general have been refractory to structure determination by crystallography. However, high-resolution structural evidence on individual separate subdomains of the insulin receptor and of analogous proteins has been obtained. The recently solved quaternary structure of the complete dimeric insulin receptor in the presence of insulin has now served as the structural envelope into which such individual domains were fitted. The combined structure has provided answers on the details of insulin/receptor interactions in the binding site and on the mechanism of transmembrane signaling of this covalent dimer. The structure explains many observations on the behavior of the receptor, from greater or lesser binding of insulin and its variants, point and deletion mutants of the receptor, to antibody-binding patterns, and to the effects on basal and insulin-stimulated autophosphorylation under mild reducing conditions.

High-pressure paint gun injury to the orbit and ocular adnexa

High-pressure injection injury to the orbit and adnexa is a rare but potentially blinding type of trauma. Few cases of such injury have been reported in the literature. A 27-year-old Indian man accidentally injected paint material from a high-pressure nozzle gun into his left eye. Radiological investigation revealed the presence of paint material in the orbital tissues and the ethmoidal sinuses. The patient underwent two orbital surgeries to remove the paint material. He later developed signs suggestive of limbal stem cell failure and was treated with limbal stem cell autografting. He also has ophthalmoplegia with a compensatory anomalous head posture that was managed conservatively. We report the clinical course and outcome of this unfortunate patient to highlight the complexity of such an injury and the need for a multidisciplinary approach in its management.

Ocular decompression retinopathy after resolution of acute primary angle closure glaucoma

A patient presented with acute primary angle closure glaucoma with markedly elevated intraocular pressure. Two weeks after laser peripheral iridotomy and resolution of the acute attack, the patient was noted to have developed scattered retinal haemorrhages. The haemorrhages resolved over time with no visual sequelae. This is the first reported case of ocular decompression retinopathy after resolution of acute primary angle closure glaucoma.

The correction of oriental lower lid involutional entropion using the combined procedure

INTRODUCTION

Involutional entropion is a common lid malposition problem in the Chinese geriatric population. The major contributing factors of involutional entropion include disinsertion of the lower lid retractors and horizontal lid laxity. The combined procedure (lower lid retractor repair and lateral tarsal strip procedure) is a useful technique that tackles both the horizontal and vertical aetiologic components of this condition. The surgical technique of this procedure is described and the results and complications presented.

MATERIALS AND METHODS

A retrospective non-randomised study on 41 lower eyelids of 38 Chinese patients. The combined procedure was performed by a single surgeon over a 2 years 11 months period. Nine patients had bilateral lid surgeries. The clinical charts and operative notes were reviewed by an observer.

RESULTS

The mean age of the patients was 74.7 years (range 51 to 92 years). There were 14 males (36.8%) and 24 females (63.2%). The cases were followed up postoperatively for a mean duration of 13 months (range 3 to 48 months). Twelve lids had early postoperative overcorrection but the majority (8 lids) resolved spontaneously with good lid-globe apposition. Of the remaining 4 eyelids, 3 lids had persistent mild asymptomatic ectropion that did not require surgical treatment and only one required re-operation.

CONCLUSION

The combined procedure is an effective means of repair for oriental lower lid entropion with low complication rates.

Comparison of the intraocular pressure-lowering effect of latanoprost and timolol in patients with chronic angle closure glaucoma: a preliminary study

OBJECTIVE

To compare the intraocular pressure (IOP)-reducing effect and side effects of 0.005% latanoprost once daily to 0.5% timolol twice daily in patients with primary chronic angle closure glaucoma (CACG).

DESIGN

Randomized, double-masked two-center clinical trial.

PARTICIPANTS

Thirty-two Asian patients with CACG, defined as glaucomatous optic neuropathy with a compatible visual field defect and at least 6 clock hours of synechial angle closure on gonioscopy were recruited. All patients had previous peripheral iridotomy (PI) with IOP >21 mmHg after PI and were thereafter controlled (IOP <22 mmHg) with one or two pressure-reducing drugs.

INTERVENTION

After a washout period, the patients were randomized to a 2-week treatment period with either placebo in the morning and 0.005% latanoprost in the evening or 0.5% timolol twice daily.

MAIN OUTCOME MEASURES

The short-term IOP reduction of latanoprost and timolol in patients with CACG. IOP was measured at baseline, and after 2, 7, and 14 days of treatment. In addition, the short-term ocular and systemic adverse events of the two drugs were evaluated.

RESULTS

Thirty patients completed the study. Two patients in the timolol group were withdrawn because of inadequate IOP control. Compared with baseline, the IOP after 2 weeks of treatment was statistically significantly reduced by 8.8 +/- 1.1 mmHg (mean +/- SEM, P < 0.001) in the latanoprost group, and by 5.7 +/- 0.9 mmHg (P < 0.001) in the timolol group. The difference in IOP reduction between the two treatment groups was 3.1 +/- 1.5 mm Hg in favor of latanoprost (P = 0.04). The main ocular adverse events reported in both treatment groups were conjunctival hyperemia and discomfort.

CONCLUSIONS

In this preliminary study, a significantly greater IOP reduction was achieved with 0.005% latanoprost once daily compared with 0.5% timolol twice daily in patients with CACG. The results suggest that latanoprost may be a therapeutic choice for the medical treatment of primary CACG.

Quaternary structure of the insulin-insulin receptor complex

The three-dimensional (3D) structure of the intrinsically dimeric insulin receptor bound to its ligand, insulin, was determined by electron cryomicroscopy. Gold-labeled insulin served to locate the insulin-binding domain. The 3D structure was then fitted with available known high-resolution domain substructures to obtain a detailed contiguous model for this heterotetrameric transmembrane receptor. The 3D reconstruction indicates that the two alpha subunits jointly participate in insulin binding and that the kinase domains in the two beta subunits are in a juxtaposition that permits autophosphorylation of tyrosine residues in the first step of insulin receptor activation.

Outcome of late probing for congenital nasolacrimal duct obstruction in Singapore children

OBJECTIVE

To evaluate the outcome of late probing in a mixed Asian children population with congenital nasolacrimal duct obstruction (CNLDO) and whether probing was associated with an increased risk of infection.

METHOD

A retrospective clinical study was conducted. A clinical diagnosis of CNLDO was defined in an infant who presented with a history of tearing and/or eye discharge up to 1 year of age with no other accompanying ocular pathology. All patients with a presumed diagnosis of CNLDO who had probing after 12 months of age were included in our study. Prior to probing, most patients had a trial of conservative treatment with massage and/or topical antibiotics. Intra-operative patency of probing was determined when metal to metal contact of the probe and forceps was achieved and/or when fluorescein dye was recovered from the nose after syringing. Successful probing was defined as a resolution of symptoms within 1 month after probing.

RESULTS

Seventeen patients involving 19 eyes fulfilled our inclusion criteria for this study. Fourteen (82%) infants were Chinese, two Malays (12%) and the remaining one Indian (6%). There were 10 males (59%) and 7 females (41%) and the mean age at probing was 2.2 years (range, 14 months to 5 years 6 months). The subjects were followed-up post-operatively for a mean duration of 21.2 months (range, 2 months to 8 years). Successful probing in our series was 89.5% (17/19 eyes). Of the two eyes with persistent tearing, one resolved with massage about 9 months after the unsuccessful probing; the other was referred to the oculoplastic service for further management.

CONCLUSION

Late probing after 13 months old appears to be an effective approach in the management of CNLDO in Asian infants.

Direct force measurements of insulin monomer-monomer interactions

Direct measurement of the forces involved in protein-protein and protein-receptor interactions can, in principle, provide insight necessary for the advancement of structural biology, molecular biology, and the development of therapeutic proteins. The protein insulin is illustrative in this respect as the mechanisms of insulin dimer dissociation and insulin-insulin receptor binding are crucial to the efficacy of insulin medications for the control of diabetes. Insulin molecules, modified with a photochemically active azido functionality on specific residues, were attached to force microscope tips and opposing mica surfaces in configurations that would either favor or disfavor dimer formation. Force curve measurements performed in buffer solution revealed the complexity of the insulin monomer-monomer interaction with multiple unbinding events occurring upon tip retraction, suggesting disruption of discrete molecular bonds at the monomer-monomer interface. Furthermore, the force curves exhibit long-range unbinding events, consistent with considerable elongation of the insulin molecule prior to dissociation. The unbinding forces observed in this study are the result of a combination of molecular disentanglement and dimer dissociation processes.

The surgical management of an advanced pterygium involving the entire cornea

PURPOSE

Conjunctival autografting is a well-established surgical procedure to prevent recurrence after pterygium excision. We described a modified technique of harvesting an annular autograft to cover a large conjunctival defect after excision of an extensive primary pterygium that involved three quadrants of the limbus.

METHODS

A 73-year-old Chinese farmer underwent an excision of an advanced right pterygium involving the entire cornea. A free donor graft was then harvested from the remaining superior bulbar conjunctiva to cover the conjunctival defect, which involved approximately-three quadrants of limbus. The undersized graft was split down the center to create an annular graft to cover the defect.

RESULTS

Postoperatively, there has been no recurrence over a total follow-up period of 11 months. Six months after the initial pterygium surgery, he underwent a successful penetrating keratoplasty for residual deep stromal scarring. Visual acuity 5 months after the penetrating keratoplasty remained stable at 6/18.

CONCLUSIONS

This case report shows that a modified technique of conjunctival autografting can be successful in preventing recurrence in an advanced pterygium after excision. Successful visual rehabilitation with a penetrating keratoplasty also was demonstrated in this patient.

Functional characterization of hybrid receptors composed of a truncated insulin receptor and wild type insulin-like growth factor 1 or insulin receptors

To assess the characteristics of hybrid receptors composed of one kinase-inactive alpha beta-insulin half-receptor and one endogenous alpha beta-insulin-like growth factor 1 (IGF-1) or insulin half-receptor, a cell line expressing an insulin receptor truncated by 365 amino acids (HIR delta 978) was studied, which lacks most of the cytoplasmic beta-subunit. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis under nonreducing conditions revealed four distinct receptor species: endogenous receptors, the more rapidly migrating HIR delta 978 homodimer, and two intermediate species representing HIR delta 978/IGF-1 hybrid receptors and HIR delta 978/IR hybrid receptors. In vivo ligand-binding affinity of the hybrid receptors was studied by receptor-ligand cross-linking, and the delta 978/IGF-1R hybrid receptor was found to have a high affinity for IGF-1, whereas its affinity for insulin was low. Autophosphorylation studies of lectin-purified receptors revealed that neither the HIR delta 978 holoreceptor nor the hybrid receptors underwent autophosphorylation in response to either ligand, despite the presence of intact IGF-1 or insulin half-receptors in the hybrids. Neither hybrid receptor underwent ligand-induced endocytosis, as assessed with the bioactive photoaffinity probes B2(2-nitro-4-azidophenylacetyl)-des-PheB1-insulin and N-epsilon B28-monoazidobenzoyl-IGF-1. In conclusion, the HIR delta 978/IGF-1R hybrid receptor has a high in vivo affinity for IGF-1 but not for insulin. Neither the delta 978/IGF-1R nor the delta 978/IR hybrids undergo autophosphorylation or ligand-induced endocytosis in response to either ligand, indicating that intramolecular trans-, rather than cis-, signal transduction is important in mediating autophosphorylation and endocytosis.

A novel guanylyl cyclase-A isoform: rat GC-A1 identification and mRNA localization to renal papilla and adrenal

Natriuretic peptides modulate systemic blood pressure, diuresis and natriuresis through the stimulation of cGMP production by guanylyl cyclase-coupled natriuretic peptide receptor-A and -B (GC-A and GC-B). A novel isoform of GC-A, GC-A1, has been identified which is the result of differential splicing of a new exon, 5a. This 9 bp sequence is predicted to add proline-cysteine-glutamine to the extracellular juxtamembrane region of the receptor protein. Transcripts for GC-A1 are expressed primarily in the renal papilla and adrenal. In these tissues, its abundance relative to GC-A was 1-2.5% as assessed by quantitative PCR.

Unusual insulin binding to cells expressing an insulin receptor mutated at cysteine 524

The involvement of cysteine 524 of the insulin receptor in an intermolecular (class I) disulfide bond between the two alpha-subunits was investigated using site-directed mutagenesis. The oligomeric structure of the mutated receptor was partially disrupted, although a significant portion of the receptor remained in its heterotetrameric form. Interestingly, the mutated insulin receptor heterotetramer was more susceptible than the wildtype receptor to reduction to heterodimers by low concentrations of dithiothreitol. Insulin binding to solubilized mutant receptors was normal and the mutant receptors had normal affinity for insulin, but insulin binding to cells expressing mutant insulin receptors displayed positive cooperativity. Cysteine 524 is most likely involved in a class I disulfide bond and receptors mutated at this site displayed unusual insulin binding properties only in the cellular environment.

Dithiothreitol stimulates insulin receptor autophosphorylation at the juxtamembrane domain

Autophosphorylation of insulin receptors from human placental membranes prepared with iodoacetamide was more than double that of control receptors prepared without iodoacetamide. Dithiothreitol (DTT) treatment of control receptors prepared without iodoacetamide resulted in increased autophosphorylation. However, DTT was without effect on insulin receptors prepared with iodoacetamide. Phosphopeptide analysis showed that while 32P-labeling of all of the phosphopeptides was increased in insulin receptors from membranes prepared with iodoacetamide, two additional phosphopeptides were detected and identified as deriving from the juxtamembrane domain, containing tyrosine residue 960. Similar results were produced by DTT treatment of control insulin receptors. These observations suggest that a thiol(s) may be involved in insulin receptor autophosphorylation in the juxtamembrane domain.

Rodent insulin receptors are immunologically different from other mammalian insulin receptors

Four monoclonal antibodies (MA-5, MA-10, MA-20, and MA-51) and one polyclonal antibody (ARS-2) against human insulin receptor were used to immunoprecipitate the insulin receptor from several species which had been photolabeled with N epsilon B29-monoazido-benzoyl-[125I]iodoinsulin. All four monoclonal antibodies immunoprecipitated human insulin receptor from human placental membranes. MA-10 and MA-51, but not MA-5 or MA-20, immunoprecipitated insulin receptors from liver plasma membranes of rabbit, guinea pig, dog, cattle, pig, and chicken. None of the monoclonal antibodies immunoprecipitated insulin receptors of rat, mouse, hamster, or chinchilla. In contrast, all of the insulin receptors were immunoprecipitated by the polyclonal anti-insulin receptor antibody, ARS-2. MA-10 and MA-51 compared with [125I]iodoinsulin for binding to guinea pig and rabbit liver plasma membranes in a fashion similar to insulin, although less effectively. MA-51 also mimicked the action of insulin by stimulating lipogenesis and autophosphorylation of the insulin receptor beta subunit in isolated rabbit adipocytes. The results suggest that insulin receptors of mammals, other than rodent, share with human insulin receptor the same epitope(s) recognized by MA-10 and MA-51. Rodent insulin receptors, with the exception of guinea pig, are different. We speculate that the difference lies in the amino acid sequence 485-599 of the alpha subunit of the insulin receptor.

Deletion of residues 485-599 from the human insulin receptor abolishes antireceptor antibody binding and influences tyrosine kinase activation

We have studied insulin and antireceptor antibody binding to mutated human insulin receptors deleted of residues 485-599 in the alpha-subunit by site-directed mutagenesis. Both normal and mutated receptors were expressed in rat HTC hepatoma cells. Cells expressing either the normal receptor or the mutated receptor retained the ability to bind insulin. In contrast to the normal receptor, however, the mutated receptor failed to interact with antireceptor alpha-subunit antibodies. The inability of the mutated receptor to interact with various antireceptor antibodies was further documented by photoaffinity labeling studies. In intact HTC cells expressing mutated receptors, basal insulin receptor tyrosine autophosphorylation was 2-fold elevated when compared to cells expressing normal receptors. In these cells, however, the response of this function to insulin was blunted. When receptors were isolated from these cells and assayed for both autophosphorylation and phosphotransferase activities toward the synthetic substrate poly(Glu, Tyr), the response to insulin was also blunted. To study the ability of the mutated receptor to transmembrane signal, insulin stimulation of S6 kinase activity was measured. In cells with mutated receptors, in concert with the insulin receptor kinase data, basal S6 kinase activity was elevated, and the response to insulin was blunted. The data suggest, therefore, that residues 485-599 in the alpha-subunit of the insulin receptor are critical for antireceptor antibody binding, but not for insulin binding. Moreover, these data suggest that residues 485-599 contain a regulatory domain for insulin regulation of receptor beta-subunit functions.

Hypopyon--an unusual sign in acute angle-closure glaucoma

The appearance of a hypopyon is an extremely uncommon finding in acute angle-closure glaucoma and only a few cases have been previously reported in the literature. We report a fifty-year-old female who, following a recent bereavement, presented with classical features of acute angle-closure glaucoma and a hypopyon. The eye developed a glaukomflecken and the patient underwent trabeculectomy, extracapsular cataract extraction and intraocular lens implantation with good post-operative results. Because hypopyon in acute angle-closure glaucoma is rare and may cause diagnostic confusion and hence therapeutic difficulties, this case is described to highlight this unusual clinical sign.

Preparation of N epsilon B28-monoazidobenzoyl insulin-like growth factor I and photoaffinity labeling of insulin-like growth factor I receptor

Recombinant human insulin-like growth factor I (hIGF-I) was reacted with azidobenzoyl hydroxysuccinimide to produce a mixture of photoactive hIGF-I derivatives. The mixture was purified by reversed-phase HPLC to yield three mono-substituted azidobenzoyl hIGF-Is. One of the derivatives was identified by amino acid sequencing as N epsilon B28-monoazidobenzoyl hIGF-I. This derivative was indistinguishable from native hIGF-I when bioassayed in Rat-1 fibroblasts. A 120-kDa band, the alpha subunit of the IGF-I receptor, was specifically labeled in Rat-1 plasma membranes by this photoprobe. The labeling of this band was reduced by hIGF-I at 1 nM and completely abolished by hIGF-I, but not insulin, at 100 nM, indicating the specificity of the photolabeling of the IGF-I receptor by this fully active IGF-I photoprobe.

Widespread co-localization of mRNAs encoding the guanylate cyclase-coupled natriuretic peptide receptors in rat tissues

Natriuretic peptides modulate vasorelaxation, diuresis, and natriuresis through the stimulation of cGMP production by the guanylate cyclase-coupled natriuretic peptide receptors, GC-A and GC-B. We used reverse transcription-polymerase chain reaction to determine the distribution of mRNA encoding both receptors in rat tissues. GC-A and GC-B transcripts were detected in all peripheral and neural tissues examined. Since the atrial natriuretic peptide gene is expressed in all these tissues, our widespread detection of GC-A and GC-B mRNAs now suggests that natriuretic peptides may act as endocrine and paracrine hormones as well as neurotransmitters via both GC-A and GC-B receptors.

Binding of mutant insulins to a mutated insulin receptor

We studied the binding of mutant insulins to both the normal human insulin receptor and an insulin receptor in which the sequence 240-250 of the receptor alpha subunit was mutated to provide an additional net positive charge. One mutant insulin (AspB10), which has an additional negative charge, bound to both types of receptors with a higher affinity than native insulin. Moreover, this mutant insulin was more effective in activating the tyrosine kinase activity of both types of receptors. This study suggests, therefore, that charge interactions between insulin and its receptor may play a role in insulin receptor binding and action.

Insulin receptors are bivalent as demonstrated by photoaffinity labeling

Insulin receptors in human placental membranes were photoaffinity-labeled with a radioactive human insulin-like growth factor I (hIGF-I) photoprobe N epsilon B28-monoazidobenzoyl 125I-hIGF-I either alone or together with a non-radioactive insulin photoprobe N epsilon B29-monoazidobenzoyl insulin. Precipitation of the solubilized receptors with anti-insulin antibody showed that receptors labeled with the radioactive hIGF-I photoprobe were detected in the immunoprecipitate only when photolabeling was carried out in the presence of the non-radioactive insulin photoprobe. Comparable results were obtained in converse experiments using a radioactive insulin photoprobe N epsilon B29-monoazidobenzoyl 125I-insulin, a non-radioactive hIGF-I photoprobe N epsilon B28-monoazidobenzoyl hIGF-I, and an antibody to hIGF-I. The amount of radioactive receptors precipitated by either the anti-insulin antibody or the anti-hIGHF-I antibody was close to the expected amount. These observations demonstrate that the insulin receptor is bivalent being capable of binding two molecules of ligand.

High-affinity insulin binding to an atypical insulin-like growth factor-I receptor in human breast cancer cells

We studied the nature of insulin receptor binding in MCF-7 breast cancer cells. In both intact cells and solubilized receptor preparations, high-affinity insulin binding was seen. However, unlabeled insulin-like growth factor-I (IGF-I) was five-fold more potent in inhibiting 125I-insulin binding than insulin itself. With monoclonal antibodies to the insulin receptor, 30% of 125I-insulin binding was inhibited. In contrast when alpha-IR3, a monoclonal antibody that recognizes typical IGF-I receptor, was employed over 60% of 125I-insulin binding was inhibited. The B29-MAB-125I-insulin photoprobe was then cross-linked to MCF-7 membranes. Cross-linking was inhibited by both unlabeled insulin and IGF-I. Further, the B29-MAB-125I-insulin photoprobe cross-linked to MCF-7 membranes was strongly immunoprecipitated by alpha-IR3. Employing sequential affinity chromatography with insulin-Affi-gel followed by insulin receptor monoclonal antibody agarose, atypical insulin binding activity was separated from insulin receptor binding activity. This atypical receptor had intrinsic tyrosine kinase activity. Both insulin and IGF-I stimulated the phosphorylation of the receptor's beta subunit. In MCF-7 cells both IGF-I and insulin stimulated [3H]thymidine incorporation; alpha-IR3 blocked all of the IGF-I effect but only 50-60% of the insulin effect. This study demonstrates in MCF-7 cells that, in addition to typical insulin and IGF-I receptors, there is another receptor that binds both insulin and IGF-I with high affinity.

The insulin-binding domain of insulin receptor is encoded by exon 2 and exon 3

Insulin receptors are disulfide-linked oligotetramers composed of two heterodimers each containing a 130-kDa alpha subunit and a 90-kDa beta subunit. Insulin binds to the extracellular alpha subunit, and in the process stimulates the autophosphorylation of the beta subunit and the expression of tyrosine kinase activity. Studies combining the use of photoaffinity labeling and immunoprecipitation with anti-peptide antibody have directly demonstrated that the cysteine-rich domain, encoded by exon 3, in the alpha subunit is part of the insulin-binding site of the receptor. Experiments with chimeric insulin receptors and chimeric insulin-like growth factor I receptors have confirmed that the cysteine-rich domain constitutes a part of the insulin-binding site. In addition, results from these experiments suggest that the N-terminal sequence, encoded by exon 2, in the alpha subunit also participates in insulin binding. In this review it is proposed that, assuming two insulin-binding sites per each holoreceptor oligotetramer, each insulin-binding domain may contain respectively two sub-domains for hydrophobic and charge contact with insulin, and that high-affinity binding would require the interaction of both subunits with the possibility of each subunit reciprocally contributing one of the sub-domains.

Insulin receptors prepared with iodoacetamide show enhanced autophosphorylation and receptor kinase activity

In this study, we found that adding iodoacetamide to the homogenization buffer used in the preparation of mouse or rat liver plasma membranes resulted in an increase of insulin receptor autophosphorylation by 4-5-fold and receptor kinase activity by about 2-fold. Similar effects were obtained with iodoacetate and p-chloromercuriphenyl sulfonate. The effect of iodoacetamide was minimal when it was added to membranes prepared without the thiol reagent. The enhancing effect of iodoacetamide on insulin receptor autophosphorylation was the result of a more than 2-fold decrease in the Km and a more than 3-fold increase in Vmax for ATP. The presence of iodoacetamide in the preparation of plasma membranes also greatly increased the solubilization of the insulin receptor from the plasma membrane by Triton X-100. We propose that iodoacetamide acts to alkylate some unknown thiols released during tissue homogenization and that in its absence these thiols formed mixed disulfides with the insulin receptor, thus adversely affecting the process of receptor activation by insulin.

Identification and characterization of the ligand-binding domain of insulin receptor by use of an anti-peptide antiserum against amino acid sequence 241-251 of the alpha subunit

We previously reported that a 23-kDa receptor proteolytic fragment containing an insulin-binding site was localized within residues 205-316 in the cysteine-rich region of the insulin receptor alpha subunit and postulated that sequence 241-251 plays a major role in insulin binding [Yip, C. C., Hsu, H., Patel, R. G., Hawley, D. M., Maddux, B. A., & Goldfine, I.D. (1988) Biochem. Biophys. Res. Commun. 157, 321-329]. In the present study, we have used an antiserum raised against a synthetic peptide containing sequence 241-251 to test this postulate and to study the role of sequence 241-251 in insulin binding. The antiserum immunoprecipitated the 23-kDa fragment, confirming our sequence assignment of this fragment. It also immunoprecipitated the intact alpha subunit of the insulin receptor that had been denatured by reduction and alkylation. However, sequence 241-251 in the native receptor was inaccessible to the antiserum since the antiserum did not block [125I]iodoinsulin binding and did not precipitate either photoaffinity-labeled insulin receptors or insulin receptors labeled with 125I. However, using a radioactive photoaffinity probe [( 125I]-AZAP-insulin) that allows cleavage and removal of insulin after photolabeling, we found that sequence 241-251 became accessible to the antiserum after removal of insulin. We conclude therefore that sequence 241-251 forms part of the insulin-binding domain of the insulin receptor and that the binding of insulin to the receptor induces a conformational change that allows exposure of this domain after removal of insulin. Such a conformational change may play a role in activation of the receptor and transmembrane signaling.

HeLa cells contain the atrial natriuretic peptide receptor with guanylate cyclase activity

Receptors for atrial natriuretic peptide (ANP) are heterogeneous: an approximately 140-kDa receptor exhibits ANP-stimulated guanylate cyclase activity whereas an approximately 65-kDa receptor is thought to act only as a clearance-storage protein. We have used photoaffinity labeling techniques to show that the human cell line, HeLa, contains predominantly the approximately 140-kDa ANP receptor. In contrast, several other cell lines contain primarily the approximately 65-kDa receptor. In HeLa cells, ANP bound specifically to high affinity binding sites (Kd approximately 2 nM) and stimulated a rapid, dose-dependent accumulation of cGMP. These cell lines can thus provide useful models to study the multiple mechanisms of ANP action.

Amino acid sequence deduced from a rat kidney cDNA suggests it encodes the Zn-peptidase aminopeptidase N

We have isolated and characterized rat kidney cDNA clones encoding a 140-kDa glycoprotein that exhibits characteristics of a cell surface Zn-peptidase. Structural features predicted for this putative kidney Zn-peptidase (KZP) are most consistent with properties previously determined for the Zn-peptidase aminopeptidase N. The deduced amino acid sequence of rat KZP is almost identical to the NH2-terminal sequence of aminopeptidase N purified from rabbit. The overall amino acid composition predicted for rat KZP is remarkably similar to that previously determined for rabbit and pig aminopeptidase N. The predicted Mr of rat kidney KZP approximates the Mr of the unglycosylated form of aminopeptidase N. The topology predicted for KZP is identical to that observed for aminopeptidase N: a short cytoplasmic domain at the NH2 terminus immediately precedes an uncleaved signal/anchor domain; a stalk region connects this membrane anchor to the extracellular, hydrophilic bulk of the protein containing catalytic sites required for Zn-peptidase activity. In addition, mRNA encoding KZP is present in tissues known to exhibit aminopeptidase N activity. Taken together with the observation that only a single gene homologous to KZP DNA is present in the rat and human genomes, these results suggest that we have established the primary structure of rat kidney aminopeptidase N.

Localization of the insulin-binding site to the cysteine-rich region of the insulin receptor alpha-subunit

Affinity-purified insulin receptor was photoaffinity labeled with a cleavable radioactive insulin photoprobe. Exhaustive digestion of the labeled alpha-subunit with endoproteinase Glu-C produced a major radioactive fragment of 23 kDa as a part of the putative insulin-binding domain. This fragment could contain either residues 205-316 or 518-633 of the alpha-subunit. Rat hepatoma cells and Chinese hamster ovary cells were transfected with cDNA encoding a human insulin receptor mutant with a deletion of the cysteine-rich region spanning amino acid residues 124-319. Insulin binding by these cells was not increased in spite of high numbers of the mutant insulin receptors being expressed. A panel of monoclonal antibodies which was specific for the receptor alpha-subunit and inhibited insulin binding immunoprecipitated the photolabeled 23-kDa receptor fragment but not the receptor mutant. A synthetic peptide containing residues 243-251 was specifically bound by agarose-insulin beads. We therefore suggest that the 23-kDa fragment contains residues 205-316, and that insulin binding occurs, in part, in the cysteine-rich region of the alpha-subunit.

Cell-membrane hormone receptors: some perspectives on their structure and function relationship

There are three structural regions common to hormone receptors on the cell membrane: an external region containing the ligand-specific binding domain, a hydrophobic region transversing the membrane, and a cytoplasmic region involved in the expression of activity. The structural features of these regions are broadly reviewed in regard to their functional roles. It is suggested that the specificity of cellular response to hormonal stimulation lies not only in the binding of a specific ligand by the external domain but also in the cytoplasmic region of a receptor. The cytoplasmic region can either interact specifically with a regulatory system or express its own specific ligand-dependent catalytic activity. The fundamental question of how ligand binding can lead to the expression and regulation of receptor activity is considered.

Tyrosine phosphorylation of two cytosolic proteins of 50 kDa and 35 kDa in rat liver by insulin-receptor kinase in vitro

Insulin-receptor tyrosine kinase can phosphorylate a variety of artificial substrates in vitro. Its physiological substrate(s), however, remains unknown. In the present study, we show that immobilized insulin receptors phosphorylate tyrosine residues of two cytosolic proteins of 50 kDa and 35 kDa in rat liver. Phosphorylation of these two proteins required Mn2+- or Mg2+-ATP as the phosphate donor. Phosphorylation was time- and temperature-dependent. Furthermore, the rate of phosphorylation of the two proteins was related to the autophosphorylated state of the insulin receptor. The pI of the phosphorylated 50 kDa and 35 kDa proteins was 5.4 and 5.6 respectively. These proteins were present in low abundance. They were not related to each other, nor to the insulin receptor, as demonstrated by in-gel proteolytic digestion and by immunoprecipitation using antibodies produced against them. They were specific substrates for the insulin receptor kinase, since they were not phosphorylated by epidermal-growth-factor-receptor kinase. These observations suggest that the 50 kDa and 35 kDa cytosolic proteins may be endogenous substrates for the insulin-receptor kinase.

Interaction of insulin with its receptor. I. Possible role of a histidine-arginine interaction

The interaction of beef and pork insulin with its receptors on rat liver plasma membranes has been studied as a function of pH in tris buffer. The dissociation binding constant decreased from 6.5 to 1.2 nM as the pH was increased from 6.8 to 7.8. Analysis indicated that this was the result of the deprotonation of a single residue with a pK'A of 7.62 at 20 degrees C. The enthalpy change associated with this deprotonation was estimated to be -7,500 cal/mol. On the basis of these parameters it is suggested that this group is a histidine residue on the surface of the insulin receptor. The positively charged group on the insulin molecule which interacts with this histidine was not either of the N-terminal residues, nor the lysine at position B-29; by elimination, it appears to be the B-22 arginine residue.

The structure of the hepatic insulin receptor and insulin binding

Hepatocytes or hepatic plasma membranes were photoaffinity-labelled with radioiodinated N epsilon B29-monoazidobenzoyl-insulin. Analysis of the samples by SDS/polyacrylamide-gel electrophoresis and autoradiography revealed the insulin receptor as a predominant band of 450 kDa. When hepatic plasma membranes were first treated with clostridial collagenase and then photolabelled, the insulin receptor appeared as a predominant band of 360 kDa. This effect of collagenase treatment on the insulin receptor was due to Ca2+-dependent heat-labile proteinases contaminating the preparation of collagenase, and it could be mimicked by elastase. The decrease in size of the insulin receptor to 360 kDa resulted from the loss of a receptor component that was inaccessible to photolabelling. In contrast, the size of the insulin receptor of intact cells was not affected by collagenase treatment. This suggests that the site sensitive to proteolysis was located on the cytoplasmic side of the plasma membrane. In hepatic plasma membranes that were treated with collagenase or elastase, and contained the 360 kDa form of the insulin receptor, the binding affinity for insulin was increased by up to 2-fold. These findings support the concept that a component which is either a part of, or closely associated with, the insulin receptor may regulate its affinity for insulin.

Photoaffinity labeling demonstrates binding between Ia molecules and nominal antigen on antigen-presenting cells

We have used radioiodinated photoreactive bovine insulin as antigen to examine the molecular nature of immunogenic complexes that form on antigen-presenting cells. The probe was allowed to bind to either insulin-presenting B-hybridoma cells, lipopolysaccharide-stimulated blasts, or bovine insulin-specific helper-T-hybridoma cells in the dark. Samples were then exposed to light to induce crosslinkage, solubilized, and analyzed by gel electrophoresis. Two protein bands at about 36 kDa and 27 kDa were specifically labeled on antigen-presenting cells but not on helper T cells. Treatment of these bands with dithiothreitol or endo-beta-N-acetylglucosaminidase F showed that each is composed of a single glycoprotein. These proteins are immunoprecipitable with haplotype-specific but not control anti-Ia antibodies. This identifies the labeled bands as the alpha and beta subunits of class II major histocompatibility antigens. We conclude that a molecular complex may form between Ia and antigen on antigen-presenting cells and that formation of this complex does not require the presence of a helper-T-cell antigen receptor.

Class I histocompatibility antigens and insulin receptors: evidence for interactions

We provide evidence for an interaction between mouse class I major histocompatibility complex antigens and insulin receptors. Antibodies against class I but not class II major histocompatibility complex antigens immunoprecipitate photoaffinity-labeled hepatic insulin receptors. Haplotype specificity is demonstrated by reciprocal precipitation using anti-class I antibodies and three strains of mice. Antibodies against the 45-kDa products of either the H-2K or H-2D locus and rabbit anti-mouse beta 2-microglobulin antibodies were shown to precipitate insulin receptors. We also demonstrate the specific binding of 125I-labeled insulin and 125I-labeled epidermal growth factor, but not 125I-labeled glucagon or 125I-labeled atrial natriuretic factor, to solubilized plasma membranes immunoprecipitated with anti-H-2K antibody. These observations suggest a specific interaction between class I major histocompatibility complex antigens and certain hormone receptors.

High molecular weight forms of the insulin receptor

The insulin receptor of liver, adipose, and placental plasma membranes was photoaffinity labeled with radioiodinated N epsilon B29-(monoazidobenzoyl)insulin. Three specifically labeled bands of 450, 360, and 260 kilodaltons (kDa) were identified in each tissue by polyacrylamide gel electrophoresis of the membranes solubilized in sodium dodecyl sulfate (SDS). The 360- and 260-kDa bands corresponded to partially reduced forms of the 450-kDa band. The distribution of radioactivity between the three insulin receptor bands was dependent on the tissue, the purity of the receptor preparation, and the conditions of solubilization in SDS. The 360- and 260-kDa bands became more prominent in each tissue with an increasing time of solubilization in SDS. However, with a short solubilization time in SDS, the 450-, 360-, and 260-kDa bands of the receptor were distributed approximately in a ratio of 85:15:0 in all three tissues. Inclusion of sulfhydryl alkylating reagents during solubilization in SDS altered this ratio to about 95:5:0. We conclude that the 450-kDa band represents the predominant form of the photolabeled insulin receptor and that the 260-kDa and probably the 360-kDa form as well were generated during the experimental manipulations preceding identification of the receptor. However, the appearance of the 360- and 260-kDa bands was not due to reductant present in SDS or buffer solutions and could not be accounted for by proteolytic degradation of the receptor. Furthermore, purification of the receptor over 2000-fold did not prevent the appearance of the 360- and 260-kDa bands.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptide mapping of the insulin-binding site of the 130-kDa subunit of the insulin receptor by means of a novel cleavable radioactive photoprobe

A radioactive photoaffinity probe for the insulin receptor was prepared by derivatizing insulin at its B29 lysine with a novel crosslinking reagent having a cleavable azo linkage. Insulin receptors purified from human placental membranes were photoaffinity labeled with this probe. The photolabeled receptor was treated with dithionite to cleave the azo linkage, thereby removing the insulin ligand and transferring the radioactivity to the receptor protein. The radioactive labeled subunit was isolated and digested with elastase for peptide mapping and separation by high performance liquid chromatography. Results obtained indicated that it will be feasible to use this new photoaffinity probe to obtain radioactive peptides representing the insulin-binding site(s) on the receptor subunit.