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Final report on the safety assessment of benzaldehyde.

Benzaldehyde is an aromatic aldehyde used in cosmetics as a denaturant, a flavoring agent, and as a fragrance. Currently used in only seven cosmetic products, its highest reported concentration of use was 0.5% in perfumes. Benzaldehyde is a generally regarded as safe (GRAS) food additive in the United States and is accepted as a flavoring substance in the European Union. Because Benzaldehyde rapidly metabolizes to Benzoic Acid in the skin, the available dermal irritation and sensitization data demonstrating no adverse reactions to Benzoic Acid were considered supportive of the safety of Benzaldehyde. Benzaldehyde is absorbed through skin and by the lungs, distributes to all well-perfused organs, but does not accumulate in any specific tissue type. After being metabolized to benzoic acid, conjugates are formed with glycine or glucuronic acid, and excreted in the urine. Little acute toxicity was seen. The oral LD(50) of Benzaldehyde in rats and mice ranged from 800 to 2850 mg/kg. The intraperitoneal LD(50) in white rats was 3265 mg/kg. In short-term oral studies, the no observed adverse effect level (NOAEL) was 400 mg/kg in rats and mice. In subchronic oral studies, the NOAEL was 400 mg/kg in rats and 600 mg/kg in mice. In a 16-week feeding study, rats given up to 10,000 ppm showed no signs of toxicity. Repeated inhalation of volatilized Benzaldehyde produced ocular and nasal irritation at 500 ppm and death in rabbits at 750 ppm. Undiluted Benzaldehyde was irritating to rabbit eyes, causing edema, erythema, and pain. Benzaldehyde was determined not to be a contact sensitizer, but did produce allergic reactions in a maximization test. Clinical reports of allergy to Benzaldehyde are rare. Benzoic Acid did not produce irritation or sensitization reactions in human clinical studies. Benzoic Acid also failed to produce reactions in phototoxicity and photosensitization tests. Neither Benzaldehyde, Benzoic Acid, nor Sodium Benzoate are reproductive or developmental toxicants at doses that are nontoxic to the mother. In a behavioral study, blood levels of 0.12 ng/ml Benzaldehyde produced a 44% reduction in motor activity in mice. Benzaldehyde did not produce mutations in bacterial assays, but did produce chromosomal abnormalities in Chinese hamster cells and increased mutations in a mouse lymphoma forward mutation assay. Benzaldehyde was evaluated by the National Toxicology Program, which found no evidence of carcinogenicity in rats, and some evidence of carcinogenicity in mice. Several studies have suggested that Benzaldehyde can have carcinostatic or antitumor properties. Overall, at the concentrations used in cosmetics, Benzaldehyde was not considered a carcinogenic risk to humans. Although there are limited irritation and sensitization data available for Benzaldehyde, the available dermal irritation and sensitization data and ultraviolet (UV) absorption and phototoxicity data demonstrating no adverse reactions to Benzoic Acid support the safety of Benzaldehyde as currently used in cosmetic products.

Animals↗

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus. Substrate specificities and inhibition studies.

The apparent Km and maximum velocity values of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus were determined for a range of alcohols and aldehydes and the corresponding turnover numbers and specificity constants were calculated. Benzyl alcohol was the most effective alcohol substrate for benzyl alcohol dehydrogenase. Perillyl alcohol was the second most effective substrate, and was the only non-aromatic alcohol oxidized. The other substrates of benzyl alcohol dehydrogenase were all aromatic in nature, with para-substituted derivatives of benzyl alcohol being better substrates than other derivatives. Coniferyl alcohol and cinnamyl alcohol were also substrates. Benzaldehyde was much the most effective substrate for benzaldehyde dehydrogenase II. Benzaldehydes with a single small substituent group in the meta or para position were better substrates than any other benzaldehyde derivatives. Benzaldehyde dehydrogenase II could also oxidize the aliphatic aldehydes hexan-1-al and octan-1-al, although poorly. Benzaldehyde dehydrogenase II was substrate-inhibited by benzaldehyde when the assay concentration exceeded approx. 10 microM. Benzaldehyde dehydrogenase II, but not benzyl alcohol dehydrogenase, exhibited esterase activity with 4-nitrophenyl acetate as substrate. Both benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II were inhibited by the thiol-blocking reagents iodoacetate, iodoacetamide, 4-chloromercuribenzoate and N-ethylmaleimide. Benzyl alcohol or benzaldehyde respectively protected against these inhibitions. NAD+ also gave some protection. Neither benzyl alcohol dehydrogenase nor benzaldehyde dehydrogenase II was inhibited by the metal-ion-chelating agents EDTA, 2,2'-bipyridyl, pyrazole or 2-phenanthroline. Neither enzyme was inhibited by a range of plausible metabolic inhibitors such as mandelate, phenylglyoxylate, benzoate, succinate, acetyl-CoA, ATP or ADP. Benzaldehyde dehydrogenase II was sensitive to inhibition by several aromatic aldehydes; in particular, ortho-substituted benzaldehydes such as 2-bromo-, 2-chloro- and 2-fluoro-benzaldehydes were potent inhibitors of the enzyme.

Acinetobacter↗

NTP Toxicology and Carcinogenesis Studies of Benzaldehyde (CAS No. 100-52-7) in F344/N Rats and B6C3F1 Mice (Gavage Studies).

Benzaldehyde is an aromatic aldehyde used in the food, beverage, pharmaceutical, perfume, soap, and dyestuff industries. NTP Toxicology and Carcinogenesis studies were conducted by administering benzaldehyde (99% pure) in corn oil by gavage to groups of F344/N rats and B6C3F1 mice of each sex for 16 days, 13 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, mouse lymphoma cells, Chinese hamster ovary (CHO) cells, and Drosophila melanogaster. Sixteen-Day Studies: All rats that received 1,600 mg/kg died by day 2, and 2/5 males and 2/5 females that received 800 mg/kg died before the end of the studies. Final mean body weights of dosed and vehicle control rats were similar, with the exception of the 800 mg/kg groups, in which males were 14% lighter and females were 11% lighter than vehicle controls. All mice that received 1,600 or 3,200 mg/kg died by day 3. Final mean body weights of dosed and vehicle control mice were similar. No gross lesions attributable to benzaldehyde were detected upon necropsy. Thirteen-Week Studies: Six of 10 male rats and 3/10 female rats that received 800 mg/kg and 1/10 female rats that received 400 mg/kg died near the end of the studies. Final mean body weights of dosed and vehicle control rats were similar, with the exception of male rats receiving 800 mg/kg, which were 26% lighter than vehicle controls. Compound-related lesions seen in rats receiving 800 mg/kg, but not in those receiving 400 mg/kg, included degeneration and necrosis in the cerebellum, necrosis in the hippocampus, hyperplasia and/or hyperkeratosis in the forestomach, and degeneration or necrosis of the liver and of the tubular epithelium in the kidney. Nine of 10 male mice and 1/10 female mice that received 1,200 mg/kg benzaldehyde died by the end of the first week. Compound-related renal tubule degeneration and/or necrosis and reduction in final body weight were observed in the 600 mg/kg group of male mice. No reductions in body weight or compound-related lesions were seen in female mice. Based on observations of compound-related lesions involving the brain, forestomach, kidney, and liver of male and female rats and the kidney of male mice in the 13-week studies, 2-year studies were conducted by administering 0, 200, or 400 mg/kg benzaldehyde in corn oil by gavage, 5 days per week for 103 weeks to groups of 50 male and 50 female rats and for 104 weeks to groups of 50 male mice. Based on survival data from the 16-day and 13-week studies, groups of 50 female mice were administered 0, 300, or 600 mg/kg benzaldehyde for 103 weeks. Body Weights and Survival in the Two-Year Studies: Mean body weights of dosed rats and mice were similar to their respective vehicle controls throughout the studies. The survival of the high dose group of male rats was lower than that of the vehicle controls after 1 year; no other significant differences were observed between any groups of rats or mice (survival--male rats; vehicle control, 37/50; low dose, 29/50; high dose, 21/50; female rats: 33/50; 33/50; 29/50; male mice: 32/50; 33/50; 31/50, female mice: 30/50; 27/50; 35/50). Nonneoplastic and Neoplastic Effects in the Two-Year Studies: The only effects of benzaldehyde were those seen in the forestomach of mice. The incidences of uncommonly occurring squamous cell papillomas of the forestomach in both exposure groups were significantly greater than those in vehicle controls (male: vehicle control, 1/50; low dose, 2/50; high dose, 5/50; female: 0/50; 5/50; 6/50). The increased incidences of papillomas were accompanied by dose-related increases in the incidences in forestomach hyperplasia (male: 7/50; 8/50; 16/50; female: 12/50; 23/50; 39/50). Genetic Toxicology: Benzaldehyde was not mutagenic in six strains of S. typhimurium and did not induce chromosomal aberrations in CHO cells, with or without exogenous metabolic activation. Benzaldehyde induced increases in trifluorothymidine-resistant mouse lymphoma cells in the absence exogenous metabolic activation and increased sister chromatid exchanges in CHO cells in boexchanges in CHO cells in both the presence and absence of metabolic activation. Sex-linked recessive lethal mutations were not induced in the germ cells of adult male D. melanogaster administered benzaldehyde by feeding or by injection. Conclusions: Under the conditions of these 2-year gavage studies, there was no evidence of carcinogenic activity of benzaldehyde for male or female F344/N rats receiving 200 or 400 mg/kg per day. There was some evidence of carcinogenic activity of benzaldehyde for male or female B6C3F1 mice, as indicated by increased incidences of squamous cell papillomas and hyperplasia of the forestomach. Female rats and male and female mice might have been able to tolerate higher doses. Synonyms: artificial almond oil; artificial essential oil of almond; benzenecarbonal; benzene carbaldehyde; benzoic aldehyde; phenylmethanal

Journal Article↗

Two benzaldehyde dehydrogenases in bacterium N.C.I.B. 8250. Distinguishing properties and regulation.

Evidence is presented for the existence in bacterium N.C.I.B. 8250 of two inducible NAD(+)-linked benzaldehyde dehydrogenases. They may be distinguished in crude extracts by their different thermal stabilities at high pH values, benzaldehyde dehydrogenase I being much more heat-stable than benzaldehyde dehydrogenase II. Only benzaldehyde dehydrogenase I is activated by K(+) and certain other univalent cations. Gel-filtration experiments indicate that both enzymes have molecular weights of about 180000. Both enzymes are induced by growth on l-mandelate or phenylglyoxylate; only benzaldehyde dehydrogenase I is gratuitously induced by thiophenoxyacetate and only benzaldehyde dehydrogenase II is induced by benzyl alcohol, by benzaldehyde, and by a number of heterocyclic compounds which do not support growth. Mutants have been isolated that lack either benzaldehyde dehydrogenase II or benzyl alcohol dehydrogenase, or both of the enzymes. Results obtained in induction experiments with the wild-type bacterium N.C.I.B. 8250 and with the mutants show that benzaldehyde dehydrogenase II and benzyl alcohol dehydrogenase are co-ordinately regulated. Overall, the results suggest that benzaldehyde dehydrogenase I is associated with the metabolism of l-mandelate whereas benzaldehyde dehydrogenase II is associated with the metabolism of benzyl alcohol.

Alcaligenes↗

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus. Purification and preliminary characterization.

A quick, reliable, purification procedure was developed for purifying both benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from a single batch of Acinetobacter calcoaceticus N.C.I.B. 8250. The procedure involved disruption of the bacteria in the French pressure cell and preparation of a high-speed supernatant, followed by chromatography on DEAE-Sephacel, affinity chromatography on Blue Sepharose CL-6B and Matrex Gel Red A, and finally gel filtration through a Superose 12 fast-protein-liquid-chromatography column. The enzymes co-purified as far as the Blue Sepharose CL-6B step were separated on the Matrex Gel Red A column. The final preparations of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II gave single bands on electrophoresis under non-denaturing conditions or on SDS/polyacrylamide-gel electrophoresis. The enzymes are tetramers, as judged by comparison of their subunit (benzyl alcohol dehydrogenase, 39,700; benzaldehyde dehydrogenase II, 55,000) and native (benzyl alcohol dehydrogenase, 155,000; benzaldehyde dehydrogenase II, 222,500) Mr values, estimated by SDS/polyacrylamide-gel electrophoresis and gel filtration respectively. The optimum pH values for the oxidation reactions were 9.2 for benzyl alcohol dehydrogenase and 9.5 for benzaldehyde dehydrogenase II. The pH optimum for the reduction reaction for benzyl alcohol dehydrogenase was 8.9. The equilibrium constant for oxidation of benzyl alcohol to benzaldehyde by benzyl alcohol dehydrogenase was determined to be 3.08 x 10(-11) M; the ready reversibility of the reaction catalysed by benzyl alcohol dehydrogenase necessitated the development of an assay procedure in which hydrazine was used to trap the benzaldehyde formed by the NAD+-dependent oxidation of benzyl alcohol. The oxidation reaction catalysed by benzaldehyde dehydrogenase II was essentially irreversible. The maximum velocities for the oxidation reactions catalysed by benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II were 231 and 76 mumol/min per mg of protein respectively; the maximum velocity of the reduction reaction of benzyl alcohol dehydrogenase was 366 mumol/min per mg of protein. The pI values were 5.0 for benzyl alcohol dehydrogenase and 4.6 for benzaldehyde dehydrogenase II. Neither enzyme activity was affected when assayed in the presence of a range of salts. Absorption spectra of the two enzymes showed no evidence that they contain any cofactors such as cytochrome, flavin, or pyrroloquinoline quinone. The kinetic coefficients of the purified enzymes with benzyl alcohol, benzaldehyde, NAD+ and NADH are also presented.

Acinetobacter↗

Comparison of benzyl alcohol dehydrogenases and benzaldehyde dehydrogenases from the benzyl alcohol and mandelate pathways in Acinetobacter calcoaceticus and from the TOL-plasmid-encoded toluene pathway in Pseudomonas putida. N-terminal amino acid sequences, amino acid compositions and immunological cross-reactions.

1. N-Terminal sequences were determined for benzyl alcohol dehydrogenase, benzaldehyde dehydrogenase I and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus N.C.I.B. 8250, benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase encoded by the TOL plasmid pWW53 in Pseudomonas putida MT53 and yeast K(+)-activated aldehyde dehydrogenase. Comprehensive details of the sequence determinations have been deposited as Supplementary Publication SUP 50161 (5 pages) at the British Library Document Supply Centre, Boston Spa. Wetherby. West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1991) 273. 5. The extent of sequence similarity suggests that the benzyl alcohol dehydrogenases are related to each other and also to established members of the family of long-chain Zn2(+)-dependent alcohol dehydrogenases. Benzaldehyde dehydrogenase II from Acinetobacter appears to be related to the Pseudomonas TOL-plasmid-encoded benzaldehyde dehydrogenase. The yeast K(+)-activated aldehyde dehydrogenase has similarity of sequence with the mammalian liver cytoplasmic class of aldehyde dehydrogenases but not with any of the Acinetobacter or Pseudomonas enzymes. 2. Antisera were raised in rabbits against the three Acinetobacter enzymes and both of the Pseudomonas enzymes, and the extents of the cross-reactions were determined by immunoprecipitation assays with native antigens and by immunoblotting with SDS-denatured antigens. Cross-reactions were detected between the alcohol dehydrogenases and also among the aldehyde dehydrogenases. This confirms the interpretation of the N-terminal sequence comparisons and also indicates that benzaldehyde dehydrogenase I from Acinetobacter may be related to the other two benzaldehyde dehydrogenases. 3. The amino acid compositions of the Acinetobacter and the Pseudomonas enzymes were determined and the numbers of amino acid residues per subunit were calculated to be: benzyl alcohol dehydrogenase and TOL-plasmid-encoded benzyl alcohol dehydrogenase, 381; benzaldehyde dehydrogenase I and benzaldehyde dehydrogenase II, 525; TOL-plasmid-encoded benzaldehyde dehydrogenase, 538.

Acinetobacter↗

Purification and characterisation of TOL plasmid-encoded benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase of Pseudomonas putida.

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase, two enzymes of the xylene degradative pathway encoded by the plasmid TOL of a Gram-negative bacterium Pseudomonas putida, were purified and characterized. Benzyl alcohol dehydrogenase catalyses the oxidation of benzyl alcohol to benzaldehyde with the concomitant reduction of NAD+; the reaction is reversible. Benzaldehyde dehydrogenase catalyses the oxidation of benzaldehyde to benzoic acid with the concomitant reduction of NAD+; the reaction is irreversible. Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase also catalyse the oxidation of many substituted benzyl alcohols and benzaldehydes, respectively, though they were not capable of oxidizing aliphatic alcohols and aldehydes. The apparent Km value of benzyl alcohol dehydrogenase for benzyl alcohol was 220 microM, while that of benzaldehyde dehydrogenase for benzaldehyde was 460 microM. Neither enzyme contained a prosthetic group such as FAD or FMN, and both enzymes were inactivated by SH-blocking agents such as N-ethylmaleimide. Both enzymes were dimers of identical subunits; the monomer of benzyl alcohol dehydrogenase has a mass of 42 kDa whereas that of the monomer of benzaldehyde dehydrogenase was 57 kDa. Both enzymes transfer hydride to the pro-R side of the prochiral C4 of the pyridine ring of NAD+.

Alcohol Oxidoreductases↗

Effects of disulfiram on the oxidation of benzaldehyde and acetaldehyde in rat liver.

The in vitro oxidation of benzaldehyde and acetaldehyde was studied in liver samples from disulfiram-treated and control rats. With 25 microM substrate, both cytosol and mitochondria appeared to make a nearly equal contribution to the oxidation of benzaldehyde, whereas ca. 90% of acetaldehyde oxidation occurred in mitochondria. When the Km values for benzaldehyde with aldehyde dehydrogenase (ALDH) were determined, two Km values (3 and 120 microM) were obtained with mitochondria, but only a single Km value (25 microM) was obtained with the cytosolic fraction. The relatively high Km (2.9 mM) found with microsomes makes it unlikely that microsomes are important in the oxidation of benzaldehyde. In intact mitochondria, with 200 microM acetaldehyde or benzaldehyde the matrix space enzyme accounted for 77 and 62%, respectively, of the total ALDH activity. When the activity was determined in a mixture containing both substrates, the activity was found not to be additive, indicating that both substrates are oxidized by the same matrix space enzyme. With subcellular fractions, from livers of disulfiram-treated and control rats, a greater degree of inhibition of ALDH was obtained when acetaldehyde was a substrate compared to that with benzaldehyde in cytosol and mitochondria. Microsomal ALDH was not inhibited by disulfiram. In liver slices from rats given disulfiram, a statistically significant inhibition was found when either 25 or 250 microM acetaldehyde was used (46 and 33%). With benzaldehyde, a significant inhibition (24%) was observed only with the lower substrate concentration. Finding that both mitochondrial fractions and slices were less inhibited at the higher substrate concentration implies that the high Km enzyme is not inhibited. It can be concluded that, in rat, disulfiram inhibiting liver ALDH not only affects oxidation of acetaldehyde, but also that of benzaldehyde.

Acetaldehyde↗

Effects of benzaldehyde on protein metabolism-of human cells cultivated in vitro.

The mechanism by which the antitumour agent benzaldehyde inhibits cell growth has been investigated. Human NHIK 3025 cells were synchronized by selection of mitotic cells and the protein content at various stages of the cell cycle was recorded by use of flow cytometry. In the presence of benzaldehyde (concentrations above 0.5 mM, approximately 50 micrograms/ml) the rate of protein accumulation was reduced to the same extent throughout the cell cycle. The rates of protein synthesis and protein degradation were measured by incorporation and release, respectively, of radioactively labelled valine in exponentially growing cells. It was found that benzaldehyde primarily reduced the rate of protein synthesis, while it induced only a very small effect (reduction) on the rate of protein degradation. When comparing the rate of cell-cycle progression with the rate of protein accumulation, it was found that the median interphase duration was equal to the protein doubling time even for concentrations of benzaldehyde giving a marked reduction in the rate of protein accumulation. Similar results have been observed on these cells using the specific protein synthesis inhibitor cycloheximide. However, the two drugs have different effects during mitosis, since benzaldehyde but not cycloheximide induces a specific mitotic inhibition. It is, therefore, possible that benzaldehyde inhibits the protein synthesis by a mechanism different from that of cycloheximide, a mechanism which simultaneously results in a specific mitotic inhibition. A hypothesis is proposed on the mechanism of action of benzaldehyde: that the drug might inhibit a process in the cells which activates enzymes. Such an effect might possibly entail a reduced protein synthesis as well as a prolonged mitosis. In addition, it might also count for the reported de-transforming activity of benzaldehyde on malignant cells.

Antineoplastic Agents↗

Substrate-specificity of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase encoded by TOL plasmid pWW0. Metabolic and mechanistic implications.

The substrate-specificities of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase, encoded by TOL plasmid pWW0 of Pseudomonas putida mt-2, were determined. The rates of benzyl alcohol dehydrogenase-catalysed oxidation of substituted benzyl alcohols and reduction of substituted benzaldehydes were independent of the electronic nature of the substituents at positions 3 and 4. Substitutions at position 2 of benzyl alcohol affected the reactivity of benzyl alcohol dehydrogenase: the velocity of the benzyl alcohol dehydrogenase-catalysed oxidation was lower for compounds possessing electron-withdrawing substitutions. In the reverse reaction of benzyl alcohol dehydrogenase, none of the substitutions tested influenced the apparent kcat. values. The rates of benzaldehyde dehydrogenase-catalysed oxidation of substituted benzaldehydes were influenced by the electronic nature of the substitutions: electron-withdrawing groups at positions 3 and 4 favoured the oxidation of benzaldehydes. Substitution at position 2 of benzaldehyde greatly diminished the benzaldehyde dehydrogenase-catalysed oxidation. Substitution at position 2 with electron-donating groups essentially abolished reactivity, and only substitutions that were strongly electron-withdrawing, such as nitro and fluoro groups, permitted enzyme-catalysed oxidation. The influence of the electronic nature and the position of substitutions on the aromatic ring of the substrate on the velocity of the catalysed reactions provided some indications concerning the transition state during the oxidation of the substrates, and on the rate-limiting steps of the enzymes. Pseudomonas putida mt-2 containing TOL plasmid pWW0 cannot grow on toluene derivatives substituted at position 2, nor can it grow on 2-substituted benzyl alcohols or aldehydes. One of the reasons for this may be the substrate-specificities of the benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase.

Alcohol Oxidoreductases↗

Increased effect of benzaldehyde by exchanging the hydrogen in the formyl group with deuterium.

The effect of benzaldehyde and various deuterated forms of benzaldehyde on human cells in culture has been investigated. While deuteration of the hydrogen atoms on the phenyl ring did not influence benzaldehyde's inactivating ability even after as long as 48 h treatment, deuteration of the formyl group resulted in a compound with a stronger inactivating effect than the nondeuterated benzaldehyde. Other cellular responses, such as inhibition of protein synthesis and of cell cycle progression, were also increased with benzaldehyde-d1 as compared to benzaldehyde. Since benzaldehyde is the basis for derivatives of chemotherapeutic interest, we suggest that the deuterated form of benzaldehyde in such derivatives will improve their clinical effects.

Antineoplastic Agents↗

Selective inhibition by benzaldehyde of the uptake of nucleosides and sugar into simian virus 40-transformed cells.

The effects of benzaldehyde, which has been found in figs as a carcinostatic element, were studied on the uptake of nucleosides, 2-deoxy-D-glucose, and amino acids into simian virus 40-transformed rat fibroblast cells (SV40-transformed cells) and into the parent normal cells (normal cells). Benzaldehyde, at the concentrations of 25 to 100 microgram/ml at which the selective growth inhibition against SV40-transformed cells was revealed, markedly inhibited the uptake of thymidine, other nucleosides, and 2-deoxy-D-glucose into SV40-transformed cells without any significant inhibition of the uptake of these compounds into normal cells. The uptake of amino acids into both transformed and normal cells was not inhibited by benzaldehyde. Selectively cytotoxic benzaldehyde-related compounds such as 4-nitrobenzaldehyde, 4-acetaminobenzaldehyde, thiophene-3-carboxaldehyde, etc., showed a similar inhibitory effect on thymidine uptake. The deprivation of glucose from the incubation medium strikingly diminished the inhibitory effect of benzaldehyde on the uptake of thymidine and 2-deoxy-D-glucose into SV40-transformed cells. The intracellular adenosine 5'-triphosphate level of SV40-transformed cells was reduced to less than one-half by treatment with benzaldehyde (50 microgram/ml) in glucose-containing medium. This effect was not observed in glucose-free medium. Treatment with benzaldehyde caused no change of the intracellular adenosine 5'-triphosphate level of normal cells. Based on the above results, the selective cytotoxicity of benzaldehyde was attributed to the reduction of intracellular adenosine 5'-triphosphate level of transformed cells, accompanied by the poor uptake of thymidine, glucose, etc., into SV40-transformed cells.

Adenosine Triphosphate↗

Purification and characterization of benzaldehyde dehydrogenase I from Acinetobacter calcoaceticus.

Benzaldehyde dehydrogenase I was purified from Acinetobacter calcoaceticus by DEAE-Sephacel, phenyl-Sepharose and f.p.l.c. gel-filtration chromatography. The enzyme was homogeneous and completely free from the isofunctional enzyme benzaldehyde dehydrogenase II, as judged by denaturing and non-denaturing polyacrylamide-gel electrophoresis. The subunit Mr value was 56,000 (determined by SDS/polyacrylamide-gel electrophoresis). Estimations of the native Mr value by gel-filtration chromatography gave values of 141,000 with a f.p.l.c. Superose 6 column, but 219,000 with Sephacryl S300. Chemical cross-linking of the enzyme subunits indicated that the enzyme is tetrameric. Benzaldehyde dehydrogenase I was activated more than 100-fold by K+, Rb+ and NH4+, and the apparent Km for K+ was 11.2 mM. The pH optimum in the presence of K+ was 9.5 and the pI of the enzyme was 5.55. The apparent Km values for benzaldehyde and NAD+ were 0.69 microM and 96 microM respectively, and the maximum velocity was approx. 110 mumol/min per mg of protein. Various substituted benzaldehydes were oxidized at significant rates, and NADP+ was also used as cofactor, although much less effectively than NAD+. Benzaldehyde dehydrogenase I had an NAD+-activated esterase activity with 4-nitrophenol acetate as substrate, and the dehydrogenase activity was inhibited by a range of thiol-blocking reagents. The absorption spectrum indicated that there was no bound cofactor or prosthetic group. Some of the properties of the enzyme are compared with those of other aldehyde dehydrogenases, specifically the very similar isofunctional enzyme benzaldehyde dehydrogenase II from the same organism.

Acinetobacter↗