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At least 127 records · Page 7Linked to original sources
PubMed2004

Type IV hypersensitivity from rubber chemicals: a 15-year experience in Taiwan.

BACKGROUND: Allergic contact dermatitis from rubber chemicals is frequent but has not been reported form Asia. OBJECTIVE: To study the pattern of type IV allergy to rubber chemicals in a Chinese-based population. METHODS: A retrospective study was conducted by reviewing the patch test results of 2,235 (604 men, 1,631 women) patients from January 1986 to December 2000. RESULTS: Ninety-nine patients (4.4%) had one or more positive reactions, 42 (6.9%) men and 57 (3.5%) women. The incidence did not increase throughout the study period. Among thiuram, mercapto, carba and black-rubber mix, thiuram is the most potent sensitizer, mostly for the hand and mercapto mix for the foot. Thiuram allergy is considered occupation related, while mercapto allergy, mostly from rubber slippers, is not typically related to an occupation. A negative correlation between thiuram and carba was found despite the frequent association between these two mixes. A high risk of rubber sensitization was noted in construction, health service, transportation, agriculture and hairdressing workers. A high frequency of concomitant sensitivity to cobalt was found. CONCLUSION: This is the first statistically analyzed study of rubber chemical allergy in Asia, which supports major trends concerning rubber chemical allergy from European studies. However, wearing rubber slippers in Taiwan contributes to the high percentage of foot dermatitis. Carba should still be retained in the European standard series because of the coexistence of thiuram and carba in rubber products. The concomitant sensitization to cobalt in rubber-allergic patients needs further evaluations.

Adult↗
PubMed2004

Significant role of bacterial undecaprenyl diphosphate (C55-UPP) for rubber synthesis by Hevea latex enzymes.

Washed bottom fraction (BF) membrane-bound particles of centrifuged fresh Hevea latex were found to be very active in rubber biosynthesis (RB). The washed BF membrane (WBM) showed higher RB activity and is strongly stimulated by anionic surfactants--more by DOC than SDS. WBM enzymes system can synthesize rubber either with allylic isoprenes (higher RB) or without (lower RB). Washed rubber particles (WRP), used generally in RB assays, had very low RB activity compared to the much higher activity observed for WBM. Bacterial undecaprenyl diphoshate (C(55)-UPP) was very active allylic initiator for rubber synthesis by WBM. Comparisons of allylic UPP with the shorter ones (C(15)-FPP, C(20)-GGPP) showed that UPP was the most effective. WBM activity orders were UPP >> GGPP > FPP. The DOC activated WBM synthesized less polyprenyl intermediates (butanol extractable) but more final rubber product (toluene/hexane extract), different than FPP and GGPP. WBM enzymes were highly versatile in using diverse different allylics, but UPP was most preferable. WRP was found a little active for UPP with DOC, but still much lower than WBM. Rubber product analysis by RP-TLC with acetone/hexane solvent system showed that WBM was mostly rubber, but WRP was mainly the intermediates. Quantitative analysis showed that WBM labeled rubber was confined to the origin spot, different than WRP as mainly labeled intermediates. It was thus confirmed that the WBM plays the key role in RB functions, and not WRP as mostly reported. WBM served as the actual rubber synthesis site, and bacterial UPP was very good RB initiator.

Bacteria↗
PubMed2006

Effect of rubber flooring on claw health in lactating dairy cows housed in free-stall barns.

Multiparous dairy cows between 10 to 30 d in milk (DIM) were enrolled in a clinical trial to evaluate the effects of rubber flooring on the development of claw lesions, locomotion scores, clinical lameness, and rates of hoof growth and wear. Two groups of cows were housed in identical free-stall facilities, except that 1 pen (rubber, n = 84) had rubber alley mats covering the entire concrete floor of the pen, whereas cows in the second pen were exposed to concrete flooring (concrete, n = 82) without rubber alley mats. All cows were evaluated 3 times between 10 and 30, 74 and 94, and 110 and 130 DIM for 1) the presence of claw lesions on their rear feet, 2) the occurrence of clinical lameness based on a locomotion score, and 3) rates of claw growth and wear as observed on the dorsal wall of the right lateral claw. No differences between flooring groups at the time of enrollment were detected for lactation number, mean DIM at first examination, body condition score, and proportion of cows with claw lesions at the first examination. Odds of developing claw lesions between examinations were not different for cows exposed to the rubber surface compared with those exposed to concrete. Cows on concrete, however, had greater odds of developing or exacerbating existing heel erosion than cows on rubber flooring. Regardless of the flooring surface, the lateral claw was more likely to develop lesions than the medial claw. Odds of becoming lame by the third examination and the proportion of cows requiring therapeutic hoof trimming because of lameness were greater for concrete-exposed cows than those on rubber. Cows on rubber flooring had decreased claw growth and wear between the first and last examination compared with cows on concrete. Regardless of flooring surface, second-lactation cows had greater wear rates than those in third or greater parities. Results of our study suggest that a soft flooring surface, such as interlocking rubber, is beneficial for hoof health.

Animals↗
PubMed2001

Influence of rubber-dam on the reconstruction of proximal contacts with adhesive tooth-colored restorations.

PURPOSE: To clinically measure the influence of rubber-dam on the proximal contact strength after its reconstruction with tooth-colored restorations. MATERIALS AND METHODS: The frictional forces during the removal of a metal strip from the proximal contact area were taken as measure for the proximal contact strengths of 46 restorations (35 ceramic inlays, 11 direct composite restorations). The teeth were separated with a rubber-dam and wedged thoroughly during the complete reconstruction procedure according to the multiple wedging technique. The proximal contact strengths were measured immediately before and immediately after removing the rubber-dam. RESULTS: The contact strengths were statistically significantly lower immediately after the removal of the rubber-dam (1.07+/-0.82N) compared to the situation with the rubber-dam (1.99+/-1.21N). The amount of the reduction after removing the rubber-dam was statistically significantly higher between the second premolar and the first molar (1.45+/-1.06N) compared to the contacts between the canines and the first premolar (0.32+/-0.44N) and the first and second premolar (0.59+/-0.77N). No influence of the restorative material, the use and localization of retainers, localization of the restoration, or number of teeth under the rubber-dam was detectable. CONCLUSION: Rubber-dam is recommended for adhesive restorations as it is helpful for achieving good adhesion between the tooth and restorative materials. Nevertheless, the application of rubber-dam seems to be a factor which complicates the reconstruction of adequate proximal contacts.

Analysis of Variance↗
PubMed2003

A new rubber dam frame design--easier to use with a more secure fit.

The application of the rubber dam (dental dam) is indicated in endodontics and for restorative dental treatments involving the acid-etch technique. The frequency of the technique's use varies significantly according to individual circumstances, and is generally too low given its advantages. One possible reason for many dentists' reluctance to use it could be frustrating results in the past with technically difficult applications. Such conditions arise, for example, when the taut rubber dam sheet exerts too much pull on the rubber dam clamps, causing them (and the entire rubber dam) to come loose. Particularly susceptible here are clamps attached to molars. This undesired tension results from stretching the rubber dam material--a necessary step--for attaching the sheet to the traditional rubber dam frame. As an alternative, a new easy-to-use rubber dam frame (Safe-T-Frame) has been developed that offers a secure fit without stretching the rubber dam sheet. Instead, its "snap-shut" design takes advantage of the clamping effect on the sheet caused when its two mated frame members are firmly pressed together. In this way the sheet is securely attached, but without being stretched. Held in this manner, the dam sheet is under less tension, and hence, exerts less tugging on clamps--especially on those attached to molars. Even in cases where there are no distinct anatomic undercuts, this lack of tension in the sheet eases isolation procedures and permits the use of standard rubber dam clamps. As a further benefit, the frame's raised edging provides a barrier around the sheet, which prevents small amounts of fluids from escaping. This contributes to greater patient comfort.

Dental Stress Analysis↗
PubMed2000

Microstructure of Purified Rubber Particles.

Purified rubber particles from Hevea brasiliensis (Brazilian rubber tree), Parthenium argentatum (guayule), Ficus elastica (Indian rubber tree), and Euphorbia lactiflua were examined and compared using conventional scanning electron microscopy (SEM), field-emission SEM, cryo-SEM, and transmission electron microscopy (TEM). Rubber particles of all four species were spherical; they varied in size and had a uniform homogeneous material, the rubber core, surrounded by a contiguous monolayer (half-unit) membrane. Frozen-hydrated and/or untreated particles from H. brasiliensis and P. argentatum deformed and fused readily, whereas those from F. elastica and E. lactiflua retained their spherical shapes. These results indicate that the surface components of the H. brasiliensis and P. argentatum particles are more fluid than those of F. elastica or E. lactiflua. When fixed in aldehyde, F. elastica particles retained their spherical exterior shapes but had hollow centers, whereas H. brasiliensis and P. argentatum particles completely collapsed. In aldehyde-osmium tetroxide-fixed material, the rubber core of F. elastica was poorly preserved in some particles in which only a small amount of the rubber core remained adhering to the monolayer membrane, leaving a hollow center. Euphorbia lactiflua particles were well preserved in terms of retaining the rubber core; however, the membrane was not as easily discernible as it was in the other three species. Both H. brasiliensis and P. argentatum were well preserved following fixation; their cores remained filled with rubber, and their monolayer membranes were defined. The addition of potassium permanganate to the fixation-staining regime resulted in higher-contrast micrographs and more well defined monolayer membranes.

Journal Article↗
PubMed2006

Rubber Tree (Hevea brasiliensis Muell. Arg).

Rubber tree (Hevea brasiliensis Muell. Arg.) is an important industrial crop for natural rubber production. At present, more than 9.5 million hectares in about 40 countries are devoted to rubber tree cultivation with a production about 6.5 million tons of dry rubber each year. The world supply of natural rubber is barely keeping up with a global demand for 12 million tons of natural rubber in 2020. Tapping panel dryness (TPD) is a complex physiological syndrome widely found in rubber tree plantations, which causes severe yield and crop losses in natural rubber producing countries. Currently, there is no effective prevention or treatment for this serious malady. As it is a perennial tree crop, the integration of specific desired traits through conventional breeding is both time-consuming and labour-intensive. Genetic transformation with conventional breeding is certainly a more promising tool for incorporation of agronomically important genes that could improve existing Hevea genotype. This chapter provides an Agrobacterium-mediated transformation protocol for rubber tree using immature anther-derived calli as initial explants. We have applied this protocol to generate genetically engineered plants from a high yielding Indian clone RRII 105 of Hevea brasiliensis (Hb). Calli were co-cultured with Agrobacterium tumefaciens harboring a plasmid vector containing the Hb superoxide dismutase (SOD) gene and the reporter gene used was beta-glucuronidase (GUS) gene (uidA). The selectable marker gene used was neomycin phosphotransferase (nptII) and kanamycin was used as selection agent. We found that a suitable transformation protocol for Hevea consists of a 3-d co-cultivation with Agrobacterium in the presence of 20 mM acetosyringone, 15 mM betaine HCl, and 11.55 mM proline followed by selection on medium containing 300 mg/L kanamycin. Transformed calli surviving on medium containing 300 mg/L kanamycin showed a strong GUS-positive reaction. Upon subsequent subculture into fresh media, we obtained somatic embryogenesis and germinated plantlets, which were found to be GUS positive. The integration of uidA, nptII, and HbSOD transgenes into Hevea genome was confirmed by polymerase chain reaction (PCR) as well as Southern blot analysis.

Acetophenones↗
PubMedDate not supplied

Feasibility study on the utilization of rubber latex effluent for producing bacterial biopolymers.

Rubber latex effluent is a polluting source that has a high biochemical oxygen demand (BOD). It is estimated that about 100 million liters of effluent are discharged daily from rubber processing factories. Utilization of this effluent such as the use of a coupled system not only can reduce the cost of treatment but also yield a fermentation feedstock for the production of bioplastic. This study initially was carried out to increase the production of organic acids by anaerobic treatment of rubber latex effluent. It was found that through anaerobic treatment the concentration of organic acids did not increase. Consequently, separation of organic acids from rubber latex effluent by anion exchange resin was examined as a preliminary study of recovering acetic and propionic acids. However, the suspended solids (SS) content in the raw effluent was rather high which partially blocked the ion-exchange columns. Lime was used to remove the SS in the rubber latex effluent. After the lime precipitation process, organic acids were found to adsorb strongly onto the anion exchange resin. Less adsorption of organic acids onto the resin was observed before the lime precipitation. This was probably due to more sites being occupied by colloidal particles on the resin thus inhibiting the adsorption of organic acids. The initial concentration of organic acids in the raw effluent was 3.9 g/L. After ion exchange, the concentration of the organic acids increased to 27 g/L, which could be utilized for production of polyhydroxyalkanoates (PHA). For PHA accumulation stage, concentrated rubber latex effluent obtained from ion exchange resins and synthetic acetic acid were used as the carbon source. Quantitative analyses from fed batch culture via HPLC showed that the accumulation of PHA in Alcaligenes eutrophus was maximum with a concentration of 1.182 g/L when cultivated on synthetic acetic acid, corresponding to a yield of 87% based on its cell dry weight. The dry cell weight increased from 0.71 to 1.67 g/L. On the other hand, using concentrated rubber latex effluent containing acetic and propionic acids resulted in reduced PHA content by dry weight (14%) but the dry cell weight increased from 0.49 to 1.30 g/L. The results clearly indicated that the cells grow well in rubber latex effluent but no PHA was accumulated. This could be due to the high concentration of propionic acid in culture broth or other factors such as heavy metals. Thus further work is required before rubber latex effluent can be utilized as a substrate for PHA production industrially.

Anaerobiosis↗
PubMed1987

A case-control study of skin cancer in the tire and rubber manufacturing industry.

A case-control study was conducted in the tire and rubber manufacturing industry to examine the association of squamous cell carcinoma of the skin with rubber manufacturing materials presumed to be contaminated by polycyclic aromatic hydrocarbons. Sixty-five cases were compared to 254 matched controls for exposure to carbon black, extender oils, lubricating oils, rubber solvents, and rubber stock. Both magnitude and duration of exposure were compared using data from company personnel records. Rubber stock and lubricating oils were associated with skin cancer. The relative risk (RR) associated with the highest levels of rubber stock exposure was 2.2, and with the highest level of lubricating oil exposure it was 6.5. In analysis of subgroups of study members, the associations were strongest among workers who were born after 1900 (rubber stock, RR = 11.6; lubricating oil, RR = 4.5) and among workers whose skin cancer was diagnosed before the age of seventy (rubber stock, RR = 23.2; lubricating oil, RR = 28.3).

Adult↗
PubMed1984

The rubber dam as a means to isolate contaminated peritoneal defects after colonic resection.

After colonic resections, peritoneal defects exposed to colonic flora and blood may become the seat of localized peritonitis and cause small-bowel adhesions and obstruction. In the past five years, we have seen 14 patients where one or both of these complications was anticipated for one of the following reasons: presence of an abscess cavity, local infection or accidental tear of the colon. In these patients a rubber sheet was stitched to the edges of the peritoneal defect with absorbable sutures and brought out through the abdominal wall. In all patients the rubber dam functioned as a passive drain and as a barrier between the peritoneal defect and the small bowel. Three weeks later the rubber dam was removed by traction. None of these patients developed small-bowel obstruction and no adverse effects from the rubber sheet were seen. The working mechanism of the rubber dam was investigated in female Wistar rats. After removing the peritoneum between the left kidney and pelvis, the defect was covered with a rubber dam. A capsule with a standard solution of Escherichia coli, Bacteroides fragilis, and autoclaved feces was used to initiate peritonitis under the rubber dam. The rubber proved to act as an efficient drain and barrier. No abscesses or small-bowel adhesions were seen. In the control group, 75 per cent of the animals died from generalized peritonitis or developed an abscess.

Animals↗
PubMed1986

Conventional vs. triple rubber band ligation for hemorrhoids. A prospective, randomized trial.

Two hundred five patients with symptomatic first- and second-degree hemorrhoids were randomized to receive either conventional rubber band ligation or triple rubber band ligation. In conventional rubber band ligation, the hemorrhoids were ligated at one primary site per session at intervals of four weeks until symptoms were relieved or when all three hemorrhoids were ligated. In triple rubber band ligation, all three primary hemorrhoids were ligated in a single session. After completion of treatment, the patients were examined every three months, or earlier if symptoms recurred. Both methods were effective in the treatment of early hemorrhoids and the incidence of postligation pain and complications was similar. The advantages of having the treatment completed at the initial visit in triple rubber band ligation are obvious. Furthermore, less treatment sessions were required for triple rubber band ligation to control symptoms than for conventional rubber band ligation. Triple rubber band ligation is more cost-effective and therefore is recommended.

Clinical Trials as Topic↗
PubMed1989

Rubber band ligation of hemorrhoids and rectal mucosal prolapse in constipated patients.

Rubber band ligation was used in 160 patients with internal hemorrhoids; 43 of them also had rectal anterior mucosal prolapse; 13 had prolapse alone. Two thirds of the patients underwent a single rubber band ligation and one third a double rubber band ligation in one session without anesthesia. Ninety-four required repeated ligations. A follow-up of 25 +/- 16 months (mean +/- SD) was carried out in 153 of them. Rubber band ligation was followed by prolonged bleeding in six patients and severe pain requiring removal of the rubber band in 12 patients. The complication rate decreased significantly (P less than .05) in the last 80 patients. Compared with multiple ligation, single rubber band ligation in one sitting was followed by a lower complication rate (P less than .01). Long-term results were good in 71 percent of the patients. (A formal hemorrhoidectomy was needed within two years in 6 percent.) A significantly lower recurrence rate of 9 percent was noted in those with normal bowel habits, when compared with constipated subjects whose symptoms recurred in 85 percent (P less than .001). Constipation seems to be a predictable factor in worsening the outcome of rubber band ligation. Rubber band ligation is followed by a lower complication rate when performed in a single ligation.

Constipation↗
PubMed1992

Characterization of latex antigens and allergens in surgical gloves and natural rubber by immunoelectrophoretic methods.

Allergy to natural rubber (latex) products is increasingly frequent among both medical personnel and lay subjects. Although individual antigens and allergens in latex products have not been fully characterized, they are believed to derive from the sap of the rubber tree. Rabbit IgG and human IgE antibodies against rubber proteins were used to characterize antigens and allergens in surgical latex gloves and natural rubber by crossed immunoelectrophoresis and its modifications. The results from crossed-line immunoelectrophoresis demonstrated that the surgical latex gloves had at least 10 antigens in common with natural rubber sap and ammoniated latex. In crossed radioimmunoelectrophoresis, at least six of the 10 protein antigens in the surgical glove extract and natural rubber were allergens since they bound IgE antibodies from the latex-allergic patients' sera. The surgical glove extract also demonstrated one allergen not found in natural rubber, suggesting that rubber proteins may be altered during glove manufacture.

Animals↗
PubMed1993

Type IV allergy to rubber additives: a 10-year study of 686 cases.

BACKGROUND: Rubber additives, mainly vulcanizers and antioxidants, are increasingly a cause of contact dermatitis. OBJECTIVE: The aim of the present study was to determine the frequency of type IV allergy to rubber additives. METHODS: Seven thousand patients seen during a 10-year period were evaluated. Of them, 4680 were patch tested with the standard series recommended by the Spanish Group for Research of Contact Dermatitis (GEIDC) and a series of individual rubber additives. RESULTS: A total of 686 patients (14.7% of those patch tested) had one or more positive reactions to rubber additives. Of these, 582 (84.8%) were men and 104 (15.2%) were women. The incidence of rubber sensitization was especially high among construction workers (47.0%). CONCLUSION: Rubber additives are a common cause of occupational contact dermatitis, particularly in construction workers. We postulate that rubber gloves and boots (utilized to avoid contact with sensitizing substances) themselves may be a common cause of contact dermatitis. The high incidence of allergy to some rubber additives, such as thiurams and carbas, indicates that their replacement by other less sensitizing vulcanizers is advisable.

Adolescent↗
PubMed1997

Mercury levels in plasma and urine after removal of all amalgam restorations: the effect of using rubber dams.

OBJECTIVE: The aim of the present study was to determine whether removal of all amalgam restorations might significantly affect mercury levels in plasma and urine and whether the use of rubber dams might reduce patient exposure to mercury during amalgam removal. METHODS: All amalgam restorations were removed from 18 subjects during a single treatment session in which a rubber dam was used and from 10 subjects when a rubber dam was not used. All amalgam restorations were removed by the same dentist using high-speed cutting, water coolant, and high-volume evacuation. The levels of mercury in plasma and urine were analyzed both before and during the subsequent twelve months after amalgam removal. In order to determine whether removal of all amalgam restorations might cause an exposure large enough to significantly increase the mercury levels in two indicator media for mercury exposure, i.e., plasma and urine, and to determine if the removal might cause a significant decrease in the mercury levels found over time, the one-tailed, paired Students' t-test was used. For each individual, the pre-removal levels were compared with both the levels found in plasma on d 1 and in urine on d 10, and also with the levels found 1 y after removal. Furthermore, in order to examine whether the use of rubber dams had any effect on the mercury levels found after removal, the changes in the mercury levels found were compared between the groups using the Wilcoxon-Mann-Whitney rank sum test. RESULTS: After removal of all amalgam restorations, only the non-rubber dam group showed significant increases in the mercury levels found in plasma (p = 0.012) and urine (p = 0.037). However, one year later, the mercury levels in plasma and urine had sunk significantly below the pre-removal levels for both groups. When the changes in the mercury levels found were compared between the groups, the non-rubber dam group showed a significantly higher increase of mercury in plasma than the rubber dam group the day after removal (p = 0.0010). Compared to the pre-removal mercury levels in plasma and urine, the levels found 1 y after removal of all amalgam restorations were on average 52 +/- 23% (range 4-89%) lower in plasma and 76 +/- 21% (range 20-94%) lower in urine. SIGNIFICANCE: The study showed that dental amalgam had a statistically significant impact on the mercury levels found in plasma and urine in the patients tested, and that the use of a rubber dam during removal of all amalgam restorations significantly reduced the peak of mercury in plasma following removal.

Adult↗
PubMed2002

Microbial detoxification of waste rubber material by wood-rotting fungi.

The extensive use of rubber products, mainly tires, and the difficulties to recycle those products, has resulted in world wide environmental problems. Microbial devulcanisation is a promising way to increase the recycling of rubber materials. One obstacle is that several microorganisms tested for devulcanisation are sensitive to rubber additives. A way to overcome this might be to detoxify the rubber material with fungi prior to the devulcanisation. In this study, 15 species of white-rot and brown-rot fungi have been screened with regard to their capacity to degrade an aromatic model compound in the presence of ground waste tire rubber. The most effective fungus, Resinicium bicolor, was used for detoxification of rubber material. Increase in growth of the desulfurising bacterium Thiobacillus ferrooxidans in presence of the rubber treated with Resinicium bicolor compared to untreated rubber demonstrated that detoxification with fungi is possible.

Anthraquinones↗
PubMed1999

Exposure to mutagenic airborne particulate in a rubber manufacturing plant.

Epidemiological studies conducted in the 1980s revealed that people working in the rubber manufacturing industry had an increased risk of cancer. Even now, workers employed in rubber processing are still at risk despite the measures adopted to improve their working conditions. The aim of the study was to evaluate the presence of a genotoxic risk in a rubber industry and to verify whether or not it was possible to locate the most dangerous position among the different rubber-working processes. The mutagenic activity of airborne particulate was evaluated in samples collected in the mixing department of a rubber manufacturing plant. Ambient air samples were taken over 3-h period in two stable positions near the mixing (Banbury mixer) and calendering areas. Personal air samples were taken over 2-h period during a normal workday from five workers employed in different rubber processing operations (mixing, weighing, calendering, compounding and extruding). The mutagenic activity of the air samples was determined by plate incorporation assay using Salmonella typhimurium strains (TA 98, TA 98NR, TA 100, YG 1021) with and without metabolic activation. Polycyclic aromatic hydrocarbon (PAH) concentrations were determined by high-performance liquid chromatography (HPLC); the presence of other presumable contaminants were carried out by gas chromatography-mass spectrometry (GC-MS). The results showed substantial direct and indirect frameshift mutagenicity in both ambient and personal samples. No mutagenic activity was present in S. typhimurium TA 100, except in the personal sample from a worker employed on the Banbury mixer. HPLC analysis revealed very low concentrations of PAHs. GC-MS analysis showed the presence of compounds such as azulene derivative, 1,2-dihydro-2,2,4-trimethylquinoline, N-methyl N-phenylbenzenamine, diphenylamine, bis(2-ethylhexyl)phthalate and bis(methyl-propyl)phthalate. We conclude that the high levels of mutagenic activity in ambiental and personal samples indicate the presence of substances with high genotoxic potency; no substantial differences were seen among the several rubber processing operations. PAHs were not involved in indoor pollution. GC-MS analysis revealed the presence of compounds which may be produced by high temperatures to which the raw materials are subjected during rubber manufacturing processes. These substances are potential carcinogen though their mutagen properties have not been clearly determined.

Air Pollutants, Occupational↗
PubMed2000

Rubber molecular weight regulation, in vitro, in plant species that produce high and low molecular weights in vivo.

In three rubber-producing species, in vitro, the rates of initiation and polymerization and the biopolymer molecular weight produced were affected by the concentration of farnesyl diphosphate (FPP) initiator and isopentenyl diphosphate (IPP) elongation substrate (monomer). Ficus elastica, a low molecular weight-producer in vivo, synthesized rubber polymers approximately twice the molecular weight of those made by Hevea brasiliensis or Parthenium argentatum (which produce high molecular weights in vivo), possibly due to its lower IPP Km. In all species, increasing FPP concentrations increased rubber biosynthetic rate and new molecules initiated but decreased molecular weight by competition with the allylic diphosphate (APP) end of elongating rubber molecules for the APP binding site. Increasing IPP concentrations increased rubber biosynthetic rate and rubber molecular weight, but only when FPP concentrations were below the FPP Km's or where negative cooperativity operated. In conclusion, rubber transferase is not the prime regulator of rubber molecular weight in vivo.

Algorithms↗