Internalization of insulin receptors in the isolated rat adipose cell. Demonstration of the vectorial disposition of receptor subunits

Review of Phytochemicals Present in Psidium guajava Plant and Its Mechanism of Action on Medicinal Activities

For centuries, herbal remedies have been employed to address a variety of human ailments, and Psidium guajava Linn (Myrtaceae), commonly known as guava, stands out as a noteworthy medicinal plant with significant pharmacological potential. In India, particularly in rural areas where access to conventional medicines can be limited, the various parts of the Psidium guajava plant, including its leaves, bark, roots, and fruit, have been harnessed for their therapeutic properties to tackle various health issues. Psidium guajava Linn proves to be a valuable repository of essential nutrients along with bioactive compounds such as α-terpineol, β-caryophyllene (trans-caryophyllene), rutin, α-humulene, oleanolic acid, flavonoids, and quercetin. These components exhibit diverse medicinal activities, encompassing anti-inflammatory, anti-cancer, anti-bronchitis, anti-proliferative, anti-tumor, anti-bacterial, and anti-diabetic effects. Every facet of the guava plant holds economic significance and is cultivated on a large scale. Taxonomically, Psidium guajava can be classified within the Plantae kingdom, Magnoliophyta division, Magnoliopsida class, Rosidae subclass, Myrtales order, Myrtaceae family, Myrtoideae subfamily, Myrteae tribe, Psidium genus, Guajava species. This adaptability of guava to various soils and environmental conditions facilitates relatively easy cultivation, yielding rapid fruit production. Its widespread cultivation across India is attributed to its manifold commercial applications. To comprehensively comprehend how this plant can effectively address the array of health challenges encountered by the Indian populace, this review delves into its multifaceted therapeutic properties, highlighting its significance in healthcare practices. Ongoing research endeavors by investigators continue to uncover novel medicinal attributes associated with Psidium guajava, enriching our understanding of its potential benefits.

Presence of a functional receptor for GLP-1 in osteoblastic cells, independent of the cAMP-linked GLP-1 receptor

Glucagon-like peptide 1 (GLP-1) controls glucose metabolism in extrapancreatic tissues through receptors other than the pancreatic cAMP-linked GLP-1 receptor; also, GLP-1 induces an insulin- and PTH-independent bone anabolic action in insulin-resistant and type-2 diabetic rats. Here we searched for the presence and characteristics of GLP-1 receptors in osteoblastic MC3T3-E1 cells. [(125)I]-GLP-1 specific binding to MC3T3-E1 cells was time- and temperature-dependent, reaching maximal value at 30 min at 25 degrees C; in these conditions, [(125)I]-GLP-1 binding was dissociable, and displaced by GLP-1, partially by GLP-2, but not by exendin-4 (Ex-4), exendin-9 (Ex-9), glucagon or insulin; Scatchard analysis of the unlabeled GLP-1 data showed high and low affinity binding sites; cross-linking of GLP-1 binding revealed an estimated 70 kDa band, almost undetectable in the presence of 10(-6) M GLP-1. GLP-1, Ex-9, insulin or glucagon failed to modify cellular cAMP content, while GLP-2 and Ex-4 increased it. However, GLP-1 induced an immediate hydrolysis of glycosylphosphatidylinositols (GPIs) generating short-lived inositolphosphoglycans (IPGs), and an increase in phosphatidylinositol-3 kinase (PI3K) and mitogen activated protein kinase (MAPK) activities; Ex-4 also affected GPIs, but its action was delayed with respect to that of GLP-1. This incretin was found to decrease Runx2 but increased osteocalcin gene expression, without affecting that of osteoprotegerin or the canonical Wnt pathway activity in MC3T3-E1 cells which do not express the pancreatic GLP-1 receptor. Our data demonstrate for the first time that GLP-1 can directly and functionally interact with osteoblastic cells, possibly through a GPI/IPG-coupled receptor.

Endogenous insulin signaling protects cultured neurons from oxygen-glucose deprivation-induced cell death

Curiosity surrounding the physiological relevance of neural insulin signaling has gradually developed since the discovery that nervous tissue contains both the hormone and its receptor. Similar to other receptor tyrosine kinases, ligand interaction with the insulin receptor (IR) activates a variety of intracellular signaling pathways, particularly those relevant to cellular survival. Consequently, one explanation for the presence of the insulin pathway in the brain may involve participation in the response to neuronal injury. To investigate this possibility, the present study began by examining the effect of oxygen-glucose deprivation (OGD), a well-characterized in vitro model of ischemia, on ligand-binding, surface expression, and function of the IR in cultured rat neurons that were prepared under serum-free conditions. Reduced insulin-binding was observed following OGD, although surface expression of the receptor was not altered. However, OGD did significantly decrease the ability of insulin to stimulate phosphorylation of the transmembrane IR beta-subunit, without affecting protein expression of this subunit. Subsequent experiments focused on the manner in which pharmacologically manipulating IR function affected neuronal viability after OGD. Application of the IR sensitizer metformin moderately improved neuronal viability, while the specific IR tyrosine kinase inhibitor tyrphostin A47 was able to dramatically decrease viability; both compounds acted without affecting IR surface expression. Our study suggests that not only does the IR appear to play an important role in neuronal survival, but also that neurons may actively maintain IRs on the cell surface to compensate for the OGD-induced decrease in the ability of insulin to phosphorylate its receptor.

Translocation of small preformed vesicles is responsible for the insulin activation of glucose transport in adipose cells. Evidence from the in vitro reconstitution assay

Insulin stimulates translocation of the glucose transporter isoform 4 (Glut4) from an intracellular storage compartment to the plasma membrane in fat and skeletal muscle cells. At present, the nature of the Glut4 storage compartment is unclear. According to one model, this compartment represents a population of preformed small vesicles that fuse with the plasma membrane in response to insulin stimulation. Alternatively, Glut4 may be retained in large donor membranes, and insulin stimulates the formation of transport vesicles that deliver Glut4 to the cell surface. Finally, insulin can induce plasma membrane fusion of the preformed vesicles and, also, stimulate the formation of new vesicles. In extracts of fat and skeletal muscle cells, Glut4 is predominantly found in small insulin-sensitive 60-70 S membrane vesicles that may or may not artificially derive from large donor membranes during cell homogenization. Here, we use a cell-free reconstitution assay to demonstrate that small Glut4-containing vesicles are formed from large rapidly sedimenting donor membranes in a cytosol-, ATP-, time-, and temperature-dependent fashion and, therefore, do not represent an artifact of homogenization. Thus, small insulin-responsive vesicles represent the major form of Glut4 storage in the living adipose cell. Fusion of these vesicles with the plasma membrane may be largely responsible for the primary effect of insulin on glucose transport in fat tissue. In addition, our results suggest that insulin may also stimulate the formation of Glut4 vesicles and accelerate Glut4 recycling to the plasma membrane.

GLP-1(7-36)amide binding in skeletal muscle membranes from streptozotocin diabetic rats

A higher specific binding of GLP-1(7-36)amide is found in skeletal muscle plasma membranes from adult streptozotocin (STZ)-treated rats (insulin-dependent diabetes mellitus model) and from neonatal STZ-treated rats (non insulin-dependent diabetes mellitus model), as compared to that in normal controls; no apparent change in the affinity was observed, that indicating the presence in both diabetic models of an increased number of high affinity binding sites for the peptide. The maximal specific GLP-1(7-16)amide binding in the non insulin-dependent diabetes mellitus model was found to be significantly higher than that in the insulin-dependent diabetes mellitus model. As GLP-1(7-36)amide exerts a glycogenic effect in the rat skeletal muscle, the present data suggest that the action of the peptide in the muscle glucose metabolism may be increased in states of insulin deficiency accompanied or not by insulin resistance.

Glucagon-like peptide-1 binding to rat skeletal muscle

We have found [125I]glucagon-like peptide-1(7-36)-amide-specific binding activity in rat skeletal muscle plasma membranes, with an estimated M(r) of 63,000 by cross-linking and SDS-PAGE. The specific binding was time and membrane protein concentration dependent, and displaceable by unlabeled GLP-1(7-36)-amide with an ID50 of 3 x 10(-9) M of the peptide; GLP-1(1-36)-amide also competed, whereas glucagon and insulin did not. GLP-1(7-36)-amide did not modify the basal adenylate cyclase activity in skeletal muscle plasma membranes. These data, together with our previous finding of a potent glycogenic effect of GLP-1(7-36)-amide in rat soleus muscle, and also in isolated hepatocytes, which was not accompanied by a rise in the cell cyclic AMP content, lead use to believe that the insulin-like effects of this peptide on glucose metabolism in the muscle could be mediated by a type of receptor somehow different to that described for GLP-1 in pancreatic B cells, where GLP-1 action is mediated by the cyclic AMP-adenylate cyclase system.

Specific glycosylation site mutations of the insulin receptor alpha subunit impair intracellular transport

The insulin receptor is a transmembrane protein found on multiple cell types. This receptor is synthesized as a 190-kDa proreceptor which is cleaved to produce mature alpha and beta subunits. The proreceptor contains 18 potential sites for N-linked glycosylation: 14 on the alpha subunit and 4 on the beta subunit. The codons for asparagine in the first four sites at the amino terminus of the alpha subunit were mutated to code for glutamine. This mutant receptor cDNA was stably transfected into NIH 3T3 cells. The insulin receptor produced in these cells remained in the proreceptor form; no mature alpha and beta subunits were produced. The proreceptor was slightly smaller on SDS-PAGE gels than the wild-type proreceptor and contained four less oligosaccharide chains by tryptic peptide mapping. The carbohydrate chains on the mutant proreceptor remained endoglycosidase H sensitive. However, in the presence of brefeldin A, these oligosaccharide chains could be processed to endoglycosidase H resistant chains. By immunofluorescence, the mutant proreceptor was shown to be localized to the endoplasmic reticulum. No insulin receptors could be found on the cell-surface either with cell surface labeling with biotin or with 125I-insulin binding. Thus, glycosylation of the first four N-linked glycosylation sites of the insulin receptor is necessary for the proper processing and intracellular transport of the receptor. This is in contrast to glycosylation at the four sites on the beta subunit which appear not to be important for processing but necessary for signal transduction. Therefore, N-linked glycosylation of the insulin receptor at specific sites has multiple distinctive roles.

Analysis of binding of biotinylated protoplast-release-inducing protein that induces release of gametic protoplasts in the Closterium peracerosum-strigosum-littorale complex

A protoplast-release-inducing protein (PR-IP) which is released from mating-type plus (mt(+)) cells and induces the release of gametic protoplasts from matingtype minus (mt(-)) cells of Closterium was biotinylated and then used to examine the interaction of this protein with mt(-) cells. The protoplast-release-inducing activity of PR-IP was not altered after the biotinylation. When mt(-) cells that had been pre-cultured for 24 h were incubated with biotinylated PR-IP for 6 h in nitrogen-deficient medium that contained 1% (w/v) bovine serum albumin, and then washed with the same medium, only a 19-kDa polypeptide, the smaller subunit of PR-IP, was detected in cells by the avidin and biotinylated horseradish-peroxidase macromolecular complex system. The amount of bound 19-kDa polypeptide increased with increasing doses of PR-IP and reached a maximum at around 10 nM, reflecting the protoplast-release-inducing activity. From a Scatchard plot, the dissociation constant of the polypeptide was calculated to be 2.7 · 10(-8) M. The binding of the polypeptide proceeded only after an appropriate period of pre-culture in the light, and the polypeptide was competitively displaced by non-biotinylated PR-IP. From these results, it appears that the PR-IP induces the release of protoplasts from mt(-) cells by binding of a polypeptide of relative molecular mass 19000 to the receptor on the cell surface in a manner analogous to the binding of peptide hormones in animals.

Regulation of insulin receptor functions by a peptide derived from a major histocompatibility complex class I antigen

A 25 residue peptide, Dk-(61-85), derived from the alpha 1 domain of a murine MHC class I molecule (H-2Dk), enhances cellular glucose uptake, prolongs the effect of insulin, and inhibits insulin receptor internalization without affecting insulin binding or dissociation. Full effect of the peptide is obtained at 10-100 microM. The magnitude of the peptide-mediated enhancement of glucose uptake is insulin dependent and is at maximum approximately 50% above that of full insulin stimulation, excluding a merely insulinomimetic action of the peptide. Dk-(61-85) does not interact directly with the glucose transporter molecule. Furthermore, the peptide-mediated inhibition of insulin receptor internalization results in 2-3 times more receptors in the plasma membrane. The peptide also causes hypoglycemia in rats. The biological activity of Dk-(61-85) suggests that an important nonimmunological role of MHC class I molecules is to affect some of the key functions of ligand-activated receptors.

Internalization and degradation of insulin by a human insulin receptor-v-ros hybrid in Chinese hamster ovary cells

Chinese hamster ovary cell lines expressing either the wild-type human insulin receptor or a hybrid molecule in which the tyrosine kinase domain of the insulin receptor is replaced with that of the oncogene, v-ros were examined for their ability to internalize and degrade insulin. Cells expressing the hybrid receptor were found to internalize and degrade insulin at approximately half the rate of cells expressing the native insulin receptor. Moreover, insulin was incapable of inducing the internalization of the cell-surface hybrid molecule. In contrast, the constitutive rate of receptor internalization was found to be the same for the hybrid and wild-type receptors. These results obtained were similar to those with cells expressing either wild-type or mutant receptors lacking kinase activity. In conclusion, the substitution of the specificity of tyrosine kinase of the insulin receptor with that of the v-ros oncogene product results in defective internalization and degradation of insulin, and loss of ligand-induced receptor internalization.

Insulin and insulinlike growth factor receptors regulating neurite formation in cultured human neuroblastoma cells

The functional role of brain insulin and insulinlike growth factor (IGF) receptors is being sought. Recently it has been found that these ligands are members of a newly identified family of neuritogenic polypeptides. We studied the relationship between 125I-insulin and 125I-IGF binding and their capacity to enhance neurite formation in cultured human neuroblastoma SH-SY5Y cells. The binding of 125I-insulin was temperature-dependent and heterogeneous. The Scatchard plot and dissociation rate were both consistent with the presence of two types of sites. There appeared to be about 900 high affinity sites per cell with a Kd of about 3 nM. This compared favorably with the half-maximal concentration of 4 nM for enhancement of neurite formation. The type I IGF sites were also present. Physiologic concentrations of insulin clearly enhanced neurite formation through the insulin sites, whereas physiologic concentrations of IGF-I and IGF-II enhanced through the IGF sites. Cross-occupancy of sites was observed at supraphysiologic concentrations, providing a reasonable explanation for the broad dose-response curves for these ligands. These results support the suggestion that one function of insulin and IGF receptors in neural tissues may be to modulate neurite formation.

Effects of gluconeogenic hormones on insulin binding in intact human red blood cells

The effects of gluconeogenic hormones, adrenaline and cortisol, on insulin binding were studied in intact human red blood cells. Insulin binding was significantly decreased when red blood cells were preincubated with 1.0 microgram . ml-1 adrenaline or cortisol respectively. The Scatchard plot suggested that this was due to a decrease in surface receptor concentration. Furthermore, it showed that adrenaline also increased insulin receptor affinity. The negative co-operativity affinity profile demonstrated that adrenaline caused a rise in only the upper limit average affinity, Ki, of the insulin receptor.

Generation of oligomeric insulin receptor forms by intramolecular sulfhydryl-disulfide exchange. Involvement of masked sulfhydryl groups

Insulin receptors from rat liver membranes were labelled with a 125I-labelled photoreactive insulin analogue or by iodination using lactoperoxidase and analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Under nonreducing conditions different receptor forms with Mr 400,000 (alpha 2 beta 2), 360,000 (alpha 2 beta beta'), 330,000 (alpha 2 beta' beta'), 320,000 (alpha 2 beta), 280,000 (alpha 2 beta'), 240,000 (alpha 2), 210,000 (alpha beta), 165,000 (alpha beta') and 115,000 (alpha) were detected. The subunit composition of these receptor forms was determined by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis in the absence and presence of dithioerythritol. During denaturation in sodium dodecyl sulfate in the absence of reductants, the Mr 400,000 receptor form (alpha 2 beta 2) was converted into the Mr 320,000 (alpha 2 beta) and Mr 240,000 (alpha 2) receptor form. This conversion was prevented either by N-ethylmaleimide, oxidants, or low pH. In contrast, alkylation of the receptor with N-ethylmaleimide under non-denaturing conditions did not prevent the appearance of intermediate-sized receptor forms. Furthermore, the inhibition of receptor cleavage by N-ethylmaleimide during denaturation was also observed when the amount of free sulfhydryl groups was reconstituted by the addition of an unlabelled and non-alkylated receptor sample to the alkylated and photoaffinity-labelled receptor. These results suggest, that the generation of different oligomeric receptor forms detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis is due at least in part to the cleavage of one or both beta-subunits from the insulin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and autophosphorylation of insulin receptors from rat skeletal muscle

Insulin receptors of rat skeletal muscle were purified by first extracting a plasma membrane-enriched pellet obtained from a muscle homogenate with Triton X-100, followed by WGA-Sepharose and insulin-Sepharose affinity chromatography. Routinely, 4-5 micrograms of purified receptor were obtained from 15 g of tissue. The purified receptors are composed of two major polypeptides with molecular weights of 130,000 and 95,000, respectively. The binding of [125I]insulin by the purified receptors was analyzed by a Scatchard plot. There are at least two binding components. The high-affinity component, with an apparent association constant (Ka) of 2.0 X 10(9) M-1, comprises 10% of the total insulin binding sites; while the low-affinity component, with a Ka value of 1.4 X 10(8) M-1, represents 90% of the binding sites. Assuming the insulin receptor to have a molecular weight of 300,000, the receptor binds 1.7 mol of insulin per mol at saturation. Insulin is capable of stimulating the autophosphorylation of the beta-subunit of the muscle insulin receptor (Mr 95,000) by 5-10-fold. The stoichiometry of this phosphorylation reaction was determined as 0.8 phosphate per insulin binding site after a 10 min incubation with 100 nM insulin. In a previous report, I showed that the insulin stimulation of glucose transport in diaphragms from neonatal rats was small, even although the diaphragms had normal levels of insulin receptors and glucose transporters (Wang, C. (1985). Proc. Natl. Acad. Sci. USA 82, 3621-3625). To determine whether or not receptor autophosphorylation might be related to this insensitivity to insulin, the level of receptor phosphorylation was quantitated in diaphragms from rats at different stages of development. Autophosphorylation remains unchanged from birth to 21 days of age, suggesting that the lower insulin-stimulated glucose uptake by diaphragms at early stages of postnatal development as compared to that by diaphragms of older rats, is not due to a difference in receptor kinase.

[Regulation of acinar cell receptors of the pancreas by peptides]

Peptides may act on the same receptor they regulate or on another receptor by causing regulations via receptor interactions. These receptor regulations include changes of receptor affinity and capacity. Receptor capacity is regulated by internalization, recycling, degradation, synthesis, and modification of bioavailability without migration of the receptor. Examples for those regulations, mostly based on experiments with isolated pancreatic acini from the rat, mouse, or guinea pig, are given. For the CCK receptor these examples include complex regulations of this receptor by CCK itself, bringing into discussion the hypothesis of negative cooperativity and the two-site receptor model, desensitization of the receptor by CCK, in vivo CCK influences on its receptor, and insulin receptor/CCK receptor interactions. For the insulin receptor the physiological significance of "up and down regulation" of this receptor by insulin itself is discussed. For the IGF receptors and the EGF receptor CCK-induced, Ca2+-mediated regulation of receptor internalization are another type of regulation with unknown physiological and pathophysiological significance. Finally CCK-induced, Ca2+-mediated regulation of somatostatin receptor capacity and affinity are mentioned. It is postulated that those regulations play an important role in influencing the biological effect of hormones and that knowledge about them may improve our understanding of pathophysiology.

The ligand binding subunit of the insulin-like growth factor 1 receptor has properties of a peripheral membrane protein

125I-insulin-like growth factor 1 was cross-linked to its receptor in human placenta microsomal membranes. The microsomes were treated with urea, with dithiothreitol or with both reagents prior to centrifugation at 100,000 X g. We found that greater than 80% of the label was membrane-associated following separate treatment with urea or dithiothreitol, but greater than 80% of the radioactivity remained in the supernatant after simultaneous exposure to both reagents. In identical experiments employing 125I-epidermal growth factor, no condition led to the release of greater than 10% of label from the membrane. We conclude that the ligand binding subunit of the insulin-like growth factor 1 receptor, like peripheral membrane proteins, lacks a membrane anchoring domain.

Mapping surface structures of the human insulin receptor with monoclonal antibodies: localization of main immunogenic regions to the receptor kinase domain

A panel of 37 monoclonal antibodies to the human insulin receptor has been used to characterize the receptor's major antigenic regions and their relationship to receptor functions. Three antibodies recognized extracellular surface structures, including the insulin binding site and a region not associated with insulin binding. The remaining 34 monoclonal antibodies were directed against the cytoplasmic domain of the receptor beta subunit. Competitive binding studies demonstrated that four antigenic regions (beta 1, beta 2, beta 3, and beta 4) are found on this domain. Sixteen of the antibodies were found to be directed against beta 1, nine against beta 2, seven against beta 3, and two against beta 4. Antibodies to all four regions inhibited the receptor-associated protein kinase activity to some extent, although antibodies directed against the beta 2 region completely inhibited the kinase activity of the receptor both in the autophosphorylation reaction and in the phosphorylation of an exogenous substrate, histone. Antibodies to the beta 2 region also did not recognize autophosphorylated receptor. In addition, antibodies to this same region recognized the receptor for insulin-like growth factor I (IGF-I) as well as the insulin receptor. In contrast, antibodies to other cytoplasmic regions did not recognize the IGF-I receptor as well as the insulin receptor. These results indicate that the major immunogenic regions of the insulin receptor are located on the cytoplasmic domain of the receptor beta subunit and are associated with the tyrosine-specific kinase activity of the receptor. In addition, these results suggest that a portion of the insulin receptor is highly homologous to that of the IGF-I receptor.

Colloidal gold-labeled insulin complex. Characterization and binding to adipocytes

Biologically active insulin gold complex was used as an ultrastructural marker to study insulin binding sites, uptake, and internalization in isolated rat adipocytes. The preparation conditions for monodispersed particles, ca. 16 nm in diameter and loaded with approximately 100 insulin molecules, are reported. The complex is stable for at least six weeks. Single particles or small clusters were scattered across the cell membrane. The distribution of unbound receptors seemed to be independent of the extensive system of pre-existing surface connected vesicles in adipocytes. The uptake of particles took place predominantly via non-coated pinocytotic invaginations; clathrin-coated pits did not seem to be important for this process. Lysosome-like structures contained aggregates of 10-15 particles. These data suggest that insulin gold complex is a useful marker for the specific labeling of insulin binding sites.

Urea treatment allows dithiothreitol to release the binding subunit of the insulin receptor from the cell membrane: implications for the structural organization of the insulin receptor

The sequence of the human insulin receptor has only one identifiable transmembrane region which is located in the beta subunit. The structure predicts that the alpha subunit, which binds insulin, is attached to the cell only by disulfide bonds to the beta subunit. However, treatment of membranes with dithiothreitol is ineffective at releasing the alpha subunit. If the receptor structure is unfolded with urea, dithiothreitol is able to release the alpha subunit. These data provided confirmatory evidence that the alpha subunit is not a transmembrane protein.

Degradation of insulin receptors by hepatoma cells: insulin-induced down-regulation results from an increase in the rate of basal receptor degradation

The degradation of insulin receptors was studied in cultured Zajdela hepatoma cells (ZHC). Receptor distribution within the cell was evaluated by estimating: i) surface receptor level on entire cells, ii) total cell receptors solubilized by Triton from cell membranes and iii) intracellular receptors solubilized from cells whose surface receptors had been inactivated with trypsin. In the absence of insulin, 80-90% of the insulin binding sites were located on the cell surface. When insulin was added, a rapid decrease of surface receptors was observed. After 2 h, their level was reduced nearly by half; this reduction was accounted for by an actual receptor loss from the cell without an increase in the intracellular pool. These results indicate that insulin enhanced the rate of receptor degradation within the cell. Basal receptor inactivation was studied by using tunicamycin which inhibits new receptor synthesis. The surface receptor number was decreased with a half-life of 7 h, while the level of internal sites remained unchanged. Both basal and insulin-activated receptor degradation were markedly slowed down by chloroquine or dansylcadaverine, indicating the importance of endocytic pathways in this process. Similarly, when de novo protein glycosylation was inhibited for 24 h by tunicamycin, both basal and insulin-activated receptor inactivation were precluded.(ABSTRACT TRUNCATED AT 250 WORDS)