Fine structure of the venom gland epithelium of the South American rattlesnake and radioautographic studies of protein formation by the secretory cells

Venoms and Extracellular Vesicles: A New Frontier in Venom Biology

Extracellular vesicles (EVs) are nanoparticle-sized vesicles secreted by nearly all cell types under normal physiological conditions. In toxicological research, EVs have emerged as a crucial link between public health and multi-omics approaches, offering insights into cellular responses to disease-causing injury agents such as environmental and biological toxins, contaminants, and drugs. Notably, EVs present a unique opportunity to deepen our understanding of the pathophysiology of envenomation by natural toxins. Recent advancements in isolating and purifying EV cargo, mass spectrometry techniques, and bioinformatics have positioned EVs as potential biomarkers that could elucidate biological signaling pathways and provide valuable information on the relationship between venomous toxins, their mechanisms of action, and the effectiveness of antivenoms. Additionally, EVs hold promise as proxies for various aspects of envenomation, including the toxin dosage, biological characterization, injury progression, and prognosis during therapeutic interventions. These aspects can be explored through multi-omics technology applied to EV contents from the plasma, saliva, or urine samples of envenomated individuals, offering a comprehensive integrative approach to understanding and managing envenomation cases.

A review on snake venom extracellular vesicles: Past to present

Around 95% of snake venom is protein. Along with the soluble proteins, snake venom also contains proteins encapsulated in vesicles known as Snake Venom Extracellular Vesicles (SVEV). SVEVs are nano-sized membrane-bound vesicles released from the snake venom gland cells. The available published research works on SVEVs are minimal. Extracellular vesicles in the Snake Venom gland were initially discovered during the histopathological analysis of the Crotalus durissus terrificus snakes' venom gland. Later, various techniques were employed to isolate and characterize the SVEVs. The cargo of SVEV consists of a variety of proteins like Phospholipase A-2, C-type Lectins, L-Amino Acid Oxidase, Cysteine-Rich Secretory Proteins, Serine Proteinases, Dipeptidyl Peptidase-IV, Aminopeptidase-A, Ecto-5'-nucleotidases, Disintegrins. Proteomic data revealed the presence of some exclusive proteins in the SVEVs, and the other proteins are in varying concentrations in the SVEVs compared to their whole Venom. Interaction of SVEVs with mammalian cell lines showed the disruption of primary physiological functions leads to host immune modulation, and long-term effects of envenoming. Snakebite victim's blood showed variations in the specific Extracellular vesicle concentration. It has been hypothesized that SVEVs are responsible for long-term toxicity. The current review focuses on the various techniques adopted to isolate and characterize SVEVs and discusses the exclusiveness and variations of SVEV proteins and their role in snakebites.

Extracellular Vesicles from Bothrops jararaca Venom Are Diverse in Structure and Protein Composition and Interact with Mammalian Cells

Snake venoms are complex cocktails of non-toxic and toxic molecules that work synergistically for the envenoming outcome. Alongside the immediate consequences, chronic manifestations and long-term sequelae can occur. Recently, extracellular vesicles (EVs) were found in snake venom. EVs mediate cellular communication through long distances, delivering proteins and nucleic acids that modulate the recipient cell's function. However, the biological roles of snake venom EVs, including possible cross-organism communication, are still unknown. This knowledge may expand the understanding of envenoming mechanisms. In the present study, we isolated and characterized the EVs from Bothrops jararaca venom (Bj-EVs), giving insights into their biological roles. Fresh venom was submitted to differential centrifugation, resulting in two EV populations with typical morphology and size range. Several conserved EV markers and a subset of venom related EV markers, represented mainly by processing enzymes, were identified by proteomic analysis. The most abundant protein family observed in Bj-EVs was 5'-nucleotidase, known to be immunosuppressive and a low abundant and ubiquitous toxin in snake venoms. Additionally, we demonstrated that mammalian cells efficiently internalize Bj-EVs. The commercial antibothropic antivenom partially recognizes Bj-EVs and inhibits cellular EV uptake. Based on the proteomic results and the in vitro interaction assays using macrophages and muscle cells, we propose that Bj-EVs may be involved not only in venom production and processing but also in host immune modulation and long-term effects of envenoming.

Venom production and secretion in reptiles

The venom glands of reptiles, particularly those of front-fanged advanced snakes, must satisfy conflicting biological demands: rapid synthesis of potentially labile and highly toxic proteins, storage in the gland lumen for long periods, stabilization of the stored secretions, immediate activation of toxins upon deployment and protection of the animal from the toxic effects of its own venom. This dynamic system could serve as a model for the study of a variety of different phenomena involving exocrine gland activation, protein synthesis, stabilization of protein products and secretory mechanisms. However, these studies have been hampered by a lack of a long-term model that can be propagated in the lab (as opposed to whole-animal studies). Numerous attempts have been made to extend the lifetime of venom gland secretory cells, but only recently has an organoid model been shown to have the requisite qualities of recapitulation of the native system, self-propagation and long-term viability (>1 year). A tractable model is now available for myriad cell- and molecular-level studies of venom glands, protein synthesis and secretion. However, venom glands of reptiles are not identical, and many differ very extensively in overall architecture, microanatomy and protein products produced. This Review summarizes the similarities among and differences between venom glands of helodermatid lizards and of rear-fanged and front-fanged snakes, highlighting those areas that are well understood and identifying areas where future studies can fill in significant gaps in knowledge of these ancient, yet fascinating systems.

Proteomic Identification and Quantification of Snake Venom Biomarkers in Venom and Plasma Extracellular Vesicles

The global exploration of snakebites requires the use of quantitative omics approaches to characterize snake venom as it enters into the systemic circulation. These omics approaches give insights into the venom proteome, but a further exploration is warranted to analyze the venom-reactome for the identification of snake venom biomarkers. The recent discovery of extracellular vesicles (EVs), and their critical cellular functions, has presented them as intriguing sources for biomarker discovery and disease diagnosis. Herein, we purified EV’s from the snake venom (svEVs) of Crotalus atrox and C. oreganus helleri, and from plasma of BALB/c mice injected with venom from each snake using EVtrap in conjunction with quantitative mass spectrometry for the proteomic identification and quantification of svEVs and plasma biomarkers. Snake venom EVs from C. atrox and C. o. helleri were highly enriched in 5′ nucleosidase, L-amino acid oxidase, and metalloproteinases. In mouse plasma EVs, a bioinformatic analysis for revealed upregulated responses involved with cytochrome P450, lipid metabolism, acute phase inflammation immune, and heat shock responses, while downregulated proteins were associated with mitochondrial electron transport, NADH, TCA, cortical cytoskeleton, reticulum stress, and oxidative reduction. Altogether, this analysis will provide direct evidence for svEVs composition and observation of the physiological changes of an envenomated organism.

Physiological demands and signaling associated with snake venom production and storage illustrated by transcriptional analyses of venom glands

Despite the extensive body of research on snake venom, many facets of snake venom systems, such as the physiology and regulation of the venom gland itself, remain virtually unstudied. Here, we use time series gene expression analyses of the rattlesnake venom gland in comparison with several non-venom tissues to characterize physiological and cellular processes associated with venom production and to highlight key distinctions of venom gland cellular and physiological function. We find consistent evidence for activation of stress response pathways in the venom gland, suggesting that mitigation of cellular stress is a crucial component of venom production. Additionally, we demonstrate evidence for an unappreciated degree of cellular and secretory activity in the steady state venom gland relative to other secretory tissues and identify vacuolar ATPases as the likely mechanisms driving acidification of the venom gland lumen during venom production and storage.

Snake Venom Extracellular vesicles (SVEVs) reveal wide molecular and functional proteome diversity

Proteins constitute almost 95% of snake venom's dry weight and are produced and released by venom glands in a solubilized form during a snake bite. These proteins are responsible for inducing several pharmacological effects aiming to immobilize and initiate the pre-digestion of the prey. This study shows that proteins can be secreted and confined in snake venom extracellular vesicles (SVEVs) presenting a size distribution between 50 nm and 500 nm. SVEVs isolated from lyophilized venoms collected from four different species of snakes (Agkistrodon contortrix contortrix, Crotalus atrox, Crotalus viridis and Crotalus cerberus oreganus) were analyzed by mass spectrometry-based proteomic, which allowed the identification of proteins belonging to eight main functional protein classes such as SVMPs, serine proteinases, PLA₂, LAAO, 5'nucleotidase, C-type lectin, CRISP and Disintegrin. Biochemical assays indicated that SVEVs are functionally active, showing high metalloproteinase and fibrinogenolytic activity besides being cytotoxic against HUVEC cells. Overall, this study comprehensively depicts the protein composition of SVEVs for the first time. In addition, the molecular function of some of the described proteins suggests a central role for SVEVs in the cytotoxicity of the snake venom and sheds new light in the envenomation process.

Snake venoms: attractive antimicrobial proteinaceous compounds for therapeutic purposes

Gram-positive and -negative bacteria are dangerous pathogens that may cause human infection diseases, especially due to the increasingly high prevalence of antibiotic resistance, which is becoming one of the most alarming clinical problems. In the search for novel antimicrobial compounds, snake venoms represent a rich source for such compounds, which are produced by specialized glands in the snake's jawbone. Several venom compounds have been used for antimicrobial effects. Among them are phospholipases A2, which hydrolyze phospholipids and could act on bacterial cell surfaces. Moreover, metalloproteinases and L-amino acid oxidases, which represent important enzyme classes with antimicrobial properties, are investigated in this study. Finally, antimicrobial peptides from multiple classes are also found in snake venoms and will be mentioned. All these molecules have demonstrated an interesting alternative for controlling microorganisms that are resistant to conventional antibiotics, contributing in medicine due to their differential mechanisms of action and versatility. In this review, snake venom antimicrobial compounds will be focused on, including their enormous biotechnological applications for drug development.

Peptidomics of three Bothrops snake venoms: insights into the molecular diversification of proteomes and peptidomes

Snake venom proteomes/peptidomes are highly complex and maintenance of their integrity within the gland lumen is crucial for the expression of toxin activities. There has been considerable progress in the field of venom proteomics, however, peptidomics does not progress as fast, because of the lack of comprehensive venom sequence databases for analysis of MS data. Therefore, in many cases venom peptides have to be sequenced manually by MS/MS analysis or Edman degradation. This is critical for rare snake species, as is the case of Bothrops cotiara (BC) and B. fonsecai (BF), which are regarded as near threatened with extinction. In this study we conducted a comprehensive analysis of the venom peptidomes of BC, BF, and B. jararaca (BJ) using a combination of solid-phase extraction and reversed-phase HPLC to fractionate the peptides, followed by nano-liquid chromatography-tandem MS (LC-MS/MS) or direct infusion electrospray ionization-(ESI)-MS/MS or MALDI-MS/MS analyses. We detected marked differences in the venom peptidomes and identified peptides ranging from 7 to 39 residues in length by de novo sequencing. Forty-four unique sequences were manually identified, out of which 30 are new peptides, including 17 bradykinin-potentiating peptides, three poly-histidine-poly-glycine peptides and interestingly, 10 L-amino acid oxidase fragments. Some of the new bradykinin-potentiating peptides display significant bradykinin potentiating activity. Automated database search revealed fragments from several toxins in the peptidomes, mainly from l-amino acid oxidase, and allowed the determination of the peptide bond specificity of proteinases and amino acid occurrences for the P4-P4' sites. We also demonstrate that the venom lyophilization/resolubilization process greatly increases the complexity of the peptidome because of the imbalance caused to the venom proteome and the consequent activity of proteinases on venom components. The use of proteinase inhibitors clearly showed different outcomes in the peptidome characterization and suggested that degradomic-peptidomic analysis of snake venoms is highly sensitive to the conditions of sampling procedures.

Ultrastructural and histochemical study of collagen fibres types I and III in the venom gland of Bothrops jararaca during secretory cycle

Fragments of snake (Bothrops jararaca) venom gland were analysed by light and transmission electron microscopy in order to characterize the changes in collagen fibres types I and III in the intertubular gland septa during the secretory cycle. The snakes were sacrificed at 45 days (unmilked group), 6 h, 4 and 8 days after manual extraction of the venom. The fragments were fixed, processed according to standard histologic technique for embedding in paraffin, and stained with haematoxylin-eosin and Gomori's trichrome and submitted to Gomori's silver impregnation technique and picrosirius-polarization method. For transmission electron microscopy the fragments were fixed and processed for embedding in Spurr's medium. At the 45th day (the gland at rest), when the secretory activity was at a minimum, the septa were narrow and filled with densely packed collagen fibrils. At 6 h, the septa were enlarged and exhibited wide spaces filled with finely granular Alcian Blue-positive material. Until the 8th day, the septa were narrower and the histologic aspect resembled that of the gland at rest. The results demonstrated structural modifications in the glandular septa according to the different periods of the secretory cycle. These modifications can be associated with the transformation in the secretory epithelium during the venom synthesis cycle.

Alpha1-adrenoceptors trigger the snake venom production cycle in secretory cells by activating phosphatidylinositol 4,5-bisphosphate hydrolysis and ERK signaling pathway

Loss of venom from the venom gland after biting or manual extraction leads to morphological changes in venom secreting cells and the start of a cycle of production of new venom. We have previously shown that stimulation of both alpha- and beta-adrenoceptors in the secretory cells of the venom gland is essential for the onset of the venom production cycle in Bothrops jararaca. We investigated the signaling pathway by which the alpha-adrenoceptor initiates the venom production cycle. Our results show that the alpha(1)-adrenoceptor subtype is present in venom gland of the snake. In quiescent cells, stimulation of alpha(1)-adrenoceptor with phenylephrine increased the total inositol phosphate concentration, and this effect was blocked by the phospholipase C inhibitor U73122. Phenylephrine mobilized Ca(2+) from thapsigargin-sensitive stores and increased protein kinase C activity. In addition, alpha(1)-adrenoceptor stimulation increased the activity of ERK 1/2, partially via protein kinase C. Using RT-PCR approach we obtained a partial sequence of a snake alpha(1)-adrenoceptor (260 bp) with higher identity with alpha(1D) and alpha(1B)-adrenoceptors from different species. These results suggest that alpha(1)-adrenoceptors in the venom secreting cells are probably coupled to a G(q) protein and trigger the venom production cycle by activating the phosphatidylinositol 4,5-bisphosphate and ERK signaling pathway.

Insights into and speculations about snake venom metalloproteinase (SVMP) synthesis, folding and disulfide bond formation and their contribution to venom complexity

As more data are generated from proteome and transcriptome analyses of snake venoms, we are gaining an appreciation of the complexity of the venoms and, to some degree, the various sources of such complexity. However, our knowledge is still far from complete. The translation of genetic information from the snake genome to the transcriptome and ultimately the proteome is only beginning to be appreciated, and will require significantly more investigation of the snake venom genomic structure prior to a complete understanding of the genesis of venom composition. Venom complexity, however, is derived not only from the venom genomic structure but also from transcriptome generation and translation and, perhaps most importantly, post-translation modification of the nascent venom proteome. In this review, we examine the snake venom metalloproteinases, some of the predominant components in viperid venoms, with regard to possible synthesis and post-translational mechanisms that contribute to venom complexity. The aim of this review is to highlight the state of our knowledge on snake venom metalloproteinase post-translational processing and to suggest testable hypotheses regarding the cellular mechanisms associated with snake venom metalloproteinase complexity in venoms.

Microvesicles in the venom of Crotalus durissus terrificus (Serpentes, Viperidae)

Microvesicles with electron-dense content are consistently observed by transmission electron microscopy on the luminal face of secretory cells of venom glands of viperid snakes. In this work, we evaluated their presence in Crotalus durissus terrificus venom glands and also in freshly collected venom. Microvesicles were found in the venom glands mainly in regions of exocytosis. They ranged from 40 to 80 nm in diameter. Freeze-fracture replicas of the glands revealed particles on the cytoplasmic leaflet (P-face) of these vesicles, suggesting that they carry transmembrane proteins. Vesicles separated by ultracentrifugation from cell-free venom were similar in size and structure to the microvesicles observed in the glands. A fine fuzzy coat surrounded each microvesicle. The function of these venom vesicles is still unknown, but they may contribute to inactivation of stored venom components, or their activation after the venom is released.

Venom production in long-term primary culture of secretory cells of the Bothrops jararaca venom gland

There is an increasing interest of obtaining venom by other ways than from extracting it from snakes captured in the wild. A readily available source of this venom will be useful for all pharmacological and biotechnological studies, as well as providing an improved avenue for treatments of snakebites. Here, we show that secretory cells of venom gland can be a good in vitro apparatus to produce venom. We have maintained and morphologically characterized the secretory cells of the Bothrops jararaca venom gland cultured up to 21 days. The isolated cells assemble into acini that growth in size up to 21st day, instead of adhering to the substrate. Bothropasin, a venom metalloprotease, was localized in secretory vesicles by immunoelectron microscopy and venom was also detected in culture medium in a concentration as high as 63 microg/ml. These data show that the acini formed in culture are functionally viable; they can produce and secrete venom.

Stimulation of the α-adrenoceptor triggers the venom production cycle in the venom gland of Bothrops jararaca

The noradrenergic innervation of Bothrops jararaca venom gland is thought to be important in the production and secretion of venom. We investigated the characteristics of the α-adrenoceptor in the venom gland and its role in venom production. This receptor had relatively low sensitivity to noradrenaline (pD2=4.77±0.09, N=7)and to phenylephrine (pD2=3.77±0.06, N=11). The receptor became desensitized just after venom extraction (pD2 to phenylephrine fell to 3.27±0.02, N=6) and the sensitivity remained low for at least 15 days, returning to normal 30 days after venom extraction, by which time the snake was ready for a new cycle of venom production. Incubation of secretory cells with noradrenaline(10–4 mol l–1 for 5 min) reducedα-adrenoceptor sensitivity to the level seen after venom extraction. Blockade of catecholamine production with reserpine abolished the enlargement of the rough endoplasmic reticulum and the activation of the Golgi apparatus that are normally seen after venom extraction, and the venom production was restored by a single subcutaneous (s.c.) injection of phenylephrine (100 mg kg–1) immediately after venom extraction. Our data suggest that stimulation of the α-adrenoceptor during or shortly after biting is essential for the onset of the venom production cycle.

Immunolocalization of venom metalloproteases in venom glands of adult and of newborn snakes of Bothrops jararaca

Using immunoelectronmicroscopy we analyzed qualitative and quantitatively the intracellular distribution of bothropasin, hemorrhagic factor 2 (HF2) and hemorrhagic factor 3 (HF3) in the venom secretory cells from adult snakes in the active (7 days after venom extraction) and in the resting (without venom extraction for 40 days) stages of protein synthesis. Glands from the newborn Bothrops jararaca were also studied. The results lead to the conclusion that all the secretory cells and the secretory pathway in the cells are qualitatively alike in regard to their content of the three metalloproteases. Secretory cells from the resting glands, unlike the active ones and the newborn glands, did not present immunolabeling in the narrow intracisternal spaces of the rough endoplasmic reticulum (RER). The label intensity for bothropasin was greater than that for the other proteins in the adults. HF3 and HF2 labeling densities in the newborn were higher than in the adults and HF3 labeling was not different from that of bothropasin. Co-localization of the three metalloproteases was detected in the RER cisternae of the active gland secretory cells, implying that mixing of the proteases before co-packaging into secretory vesicles occurs at the beginning of protein synthesis in the RER cisternae.

Cytochemical analysis of acid phosphatase activity in the venom secretory cells of Bothrops jararaca

A study of the histochemical reaction for acid phosphatase (AcPase) in venom gland secretory cells from Bothrops jararaca was done to investigate the distribution of lysosomes and related structures in stages of high- and low-protein synthesis. From this analysis, it was expected to gain insight into the cellular pathway by which AcPase is secreted into the venom. Two subtypes of AcPase reactivities were detected in the venom gland secretory cells: one was found in lysosomes and related structures and in some trans-Golgi network (TGN) elements and reacts with beta-glycerophosphate (betaGP) as substrate; the other was found in secretory vesicles, apical plasmalemma, lysosomes and related structures, and in some TGN elements, and reacts with cytidine monophosphate (CMP). The results are compatible with the possibility that there is a secretory via for AcPase in the venom gland of B. jararaca and that the elements composing this pathway are noted only when CMP is used as substrate. Large autophagosomes reactive to both betaGP and to CMP were commonly observed in the basal region of the secretory cells, and they were more abundant in the glands during the stage of low activity of protein synthesis.

Ultrastructure of the exocrine pancreas in the snake Waglerophis merremii (Wagler)

Three types of serozymogenic cells were found in the secretory compartment of the snake exocrine pancreas. Type I cell was the most common and presented a well-developed granular endoplasmic reticulum arranged in cisternal and vesicular forms. The cisternal form was located predominantly in the basal regions of the cell and the vesicular form was found in the supranuclear regions of the cell next to a prominent Golgi complex. Mature secretory granules were seen at the cell apex. The cytoplasmic matrix of the Type II cells was electron dense but had only poorly-developed organelles. Secretory granules were rare. The cytoplasmic matrix of the Type III cells was electron lucent and the granular endoplasmic reticulum in the cisternal form was located predominantly in the supranuclear region, whereas the vesicular form was randomly distributed throughout the cytoplasm. The nucleus appeared pale due to the fine dispersion of the chromatin; the nucleolus was prominent. Centroacinar and intermediate cells were also examined.

Ultrastructure of lingual salivary glands in the American chameleon: Anolis carolinensis

That portion of the dorsal surface of the tongue of Anolis carolinensis that is covered by plumose papillae is underlaid by a series of tubular salivary glands that open between the papillae; glands persist into the posterior zone of the tongue, where they open between cylindriform papillae. Anterior glands are serous in nature--they consist of simple columnar epithelial cells that contain abundant secretory granules exhibiting a variety of substructural patterns. The Golgi apparatus is large and of unusual appearance, with numerous closely packed terminal dilatations and condensing vacuoles. Near the posterior border of the lingual zone covered by plumose papillae, mucous cells begin to appear in the glandular epithelium. More posteriorly, the apical portions of the glands consist entirely of mucous cells, whereas the blind ends of the glands are composed of serous cells. The most posterior glands are of the pure mucous variety. The glands finally disappear a short distance posterior to the cylindriform papillae. The functions of the abundant and highly differentiated salivary glands of the Anolis tongue remain obscure.

Morphometric studies on venom secretory cells from Bothrops jararacussu (Jararacuçu) before and after venom extraction

A comparative morphometrical analysis was carried out on secretory cells from Bothrops jararacussu venom glands, before manual extraction of the venom (milking) and 4 and 8 days after milking. At the 8th day after milking, the cytoplasmic volume increased by 160%. The rough endoplasmic reticulum (RER) volume density increase, up to the 8th day after milking, is mainly due to widening of the intra-scisternal space. The total volume and membrane surface of the RER. Golgi apparatus and subcomponents, secretory vesicles and mitochondria, increased during the experimental period while the volume and surface densities of these organelles, with the exception of the RER, did not vary. The numerical density of Golgi-associated microvesicles per Golgi volume unit also increased. The greatest relative increments in these parameters occurred within the first 4 days. These results are compatible with an increased rate of membrane synthesis and transport in the milked glands and suggest that the membrane biogenesis, degradation and circulation that takes place in the first week after milking is achieved through coordinated cellular mechanisms that maintain the rate between total membrane surface and total cytoplasmic volume unaltered.

An investigation of venom secretion by the venom gland cells of the carpet viper (Echis carinatus)

The indirect immunofluorescent antibody technique was applied to the study of Echis carinatus pyramidum venom antigens in venom gland tissue using semi-thin frozen sections. A total of four rabbit antisera, two monoclonal antibodies active against E. carinatus venom, two monoclonal antibodies active against the rodent malaria parasite, Plasmodium chabaudi, and two monoclonal antibodies active against the human malaria parasite, Plasmodium falciparum, were investigated. The results of this study suggest that each secretory cell within the main part of the gland produces all the venom constituents. The resultant venom is therefore considered to be produced as a single package by each individual secretory cell. The different constituents of the venom studied are not produced at the same time or at the same rate throughout the secretory cycle, some being produced at the beginning and others at a later stage.

In vivo shedding of apical plasma membrane in the thyroid follicle cells of the mouse

Clusters of luminal dense bodies, limited by a triple-layered membrane, were found in all follicle lumina in thyroid glands of mice. After thyroxine treatment the number of luminal dense bodies increased, especially in the periphery of the lumen, where the intraluminal bodies often displayed a striking resemblance to microvilli. In hyperplastic goiters, obtained by feeding mice with propylthiouracil, luminal dense bodies were replaced by intraluminal vesicles. During goiter involution the vesicles were gradually replaced by luminal dense bodies; the presence of intermediate forms suggests that vesicles and dense bodies are basically the same formations. Luminal dense bodies were observed in colloid droplets indicating their removal by endocytosis. As demonstrated by electron-microscopic cytochemistry, luminal dense bodies contain a membrane-bound peroxidase, and electron-microscopic autoradiography after administration of 125I indicate that they possess an iodinating capacity. Our observations on mouse thyroid glands suggest that the luminal dense bodies, which appear as vesicles in hyperplastic glands, are formed by shedding of the apical plasma membrane of the follicle cell. The shedding process might be of importance for the turnover of plasma-membrane material.

Intracellular transport of proteins in active and resting secretory cells of the venom gland of Vipera palaestinae

The intracellular transport of venom proteins has been studied in active and resting venom glands of the snake Vipera palaestinae by electron microscope radioautography after an intra-arterial injection of [3H]leucine. In the active gland, most of the label is initially (10 min) found over the RER. By 30 min, the relative grain density of the Golgi complex reaches its maximum, with concomitant increase in the labeling of the condensing vacuoles. Later on, a steep increase in radioactivity of the secretory granules is observed. At 3 h, these granules, which comprise about 2% of the cell volume, contain 22% of the total grains. At the following hour, their labeling declines and at the same time the radioactivity of the secreted venom is increased. It is concluded that, in the active cell, venom proteins are transported via the Golgi apparatus into membrane-bounded granules which are the immediate source of the secreted venom. An alternative pathway, which involves the RER cisternae as a storage compartment, seems unlikely, since incorporated label does not accumulate in this compartment after prolonged postpulse intervals. The route of intracellular transport of proteins in the resting glands is similar to that of the active ones, but the rate of synthesis and transport is much slower. The present results and earlier data, thus, show that the increase in the rate of secretion after initiation of a new venom regeneration cycle is the result of accelerated rates of both synthesis and transport.

Radioautographic and biochemical studies of secretion of venom protein in the South American rattlesnake Crotalus durissus terrificus

Protein secretion was investigated in the main venom gland of the South American rattlesnake, using radioautographic and biochemical techniques after a single intracardiac injection of L-(3,5-3H)tyrosine. All the snakes were injected at the fourth day of the secretory cycle and killed at 1/2, 1, 2, 4, 8 and 24 hours after injection. Most of the radioactive amino acid is cleared from the blood stream up to four hours after injection. On the other hand the specific activity (c.p.m./mg of protein) of the intracellular proteins reaches a peak at the 4-hour time interval decreasing afterwards. There was a good correlation between the values of the specific activity of the intracellular proteins and those of the silver grain density over the secretory cells at the several time intervals after the injection of 3H-tyrosine. The results of the quantitative analysis carried out in light- and electron-microscope radioautographs led to the conclusion that venom proteins are synthesized in the rough endoplasmic reticulum of the secretory cells, transferred to the Golgi apparatus from where they are carried to the secretory tobule lumen by the secretion granules. The fact that the values of the relative concentration of the radioactivity of he intracisternal granules double at the last three time intervals, strongly suggests that these structures are formed by the aggregation of the amorphous material present inside the cisternae of the rough endoplasmic reticulum.

Characterization of ribonucleic acids from the venom glands of Crotalus durissus terrifucus (Ophidia, Reptilia) after manual extraction of the venom. Studies on template activity and base composition

RNA synthesis in the venom glands of Crotalus durissus terrificus was stimulated by the manual extraction of the venom (milking). RNA was extracted from venom glands activated by milking and fractionated by centrifugation through sucrose density gradients. Template activity for protein synthesis and base composition of the RNA fractions were studied. RNA fractions that sediment between 18S and 4S had the highest template activity. The base composition analysis indicated that the 28S and 18S rRNA have a C+G content of 65.4 and 58% respectively. The ;melting' temperature (T(m)) of DNA in 0.15m-NaCl-0.015m-trisodium citrate, pH7.0, was 85 degrees C, corresponding to a C+G content of 38%. The base ratio of the RNA fractions that showed a high template activity was intermediate between that of rRNA and homologous DNA. The possible role of these fractions in the synthesis of the two main toxins (crotoxin and crotamine) of the South American rattlesnake's venom is discussed.