The tyrosine residue at position 97 in the VH CDR3 region of a mouse/human chimeric anti-colorectal carcinoma antibody contributes hydrogen bonding to the TAG72 antigen

One amino acid, tyrosine at position 96 and 97 in the VH CDR3 region of a mouse/human chimeric anti-TAG72 antibody cB72.3m4 was substituted by the phenylalanine residue and by a number of amino acids from different amino acid groups by the site-directed mutagenesis technique. The expression vector mpSV2neo-EP1-Vm11-16C1 containing mutant VH region fragments (Vm11-16) as well as the immunoglobulin enhances (E), promoter (P1) and the human genomic C1 region fragments, were transfected into a heavy-chain-loss mutant cell line B72.3Mut(K), respectively. Mutant chimeric cB72.3m11-16 antibodies were purified from the transfectant supernates and compared based upon their binding affinity for the TAG72 antigen relative to that of the original cB72.3m4 antibody. The data showed that a single amino acid substitution of tyrosine by phenylalanine and a number of amino acids including serine, asparagine, histidine and arginine at position 97 in the VH CDR3 region all resulted in approximate 18-fold lower binding affinity, whereas the substitution of tyrosine by phenylalanine at position 96 in the VH CDR3 region did not affect the binding affinity of the cB72.3m4 antibody. This suggests that the tyrosine residue at position 97 in the VH CDR3 region is in a contact position in the B72.3/TAG72 antibody/antigen interaction, and that the terminal hydroxyl group of the position 97 tyrosine side-chain contributes hydrogen bonding to the TAG72 antigen, whereas the position 96 tyrosine side-chain does not.

[A survey of T-2 toxin in wheat by an indirect enzyme-linked immunosorbent assay]

The survey of T-2 toxin in wheat randomly sampled in nine provinces was carried out, employing an indirect competitive enzyme-linked immunosorbent assay. Among 330 samples, 264 samples (80%) showed positive results. The mean concentrations was 53.3 ppb. and maximal concentration was 1122.0 ppb. It was also detected high concentration (84.5-1064.4) of T-2 toxin in human intoxication wheat samples in 1991. The investigation also showed that there existed close relationship between the level of T-2 toxin contamination and the epidemic of wheat scabby.

Fractals and Cosmological Large-Scale Structure

Observations of galaxy-galaxy and cluster-cluster correlations as well as other large-scale structure can be fit with a "limited" fractal with dimension D approximately 1.2. This is not a "pure" fractal out to the horizon: the distribution shifts from power law to random behavior at some large scale. If the observed patterns and structures are formed through an aggregation growth process, the fractal dimension D can serve as an interesting constraint on the properties of the stochastic motion responsible for limiting the fractal structure. In particular, it is found that the observed fractal should have grown from two-dimensional sheetlike objects such as pancakes, domain walls, or string wakes. This result is generic and does not depend on the details of the growth process.

[Identification of morphology and inorganic elements of Eucommia ulmoides Oliv. produced in Sichuan by applying scanning electron microscope with energy dispersive X-ray analysis]

A research on the identification of morphology and inorganic elements of Eucommia ulmoides produced in Sichuan has been made by applying scanning electron microscope; energy dispersive X-ray analysis. Qualitative and semi-quantitative analyses of the inorganic elements in the observed areas have been obtained.

Specificity of base substitutions induced by the acridine mutagen ICR-191: mispairing by guanine N7 adducts as a mutagenic mechanism

As the most nucleophilic site in DNA, the guanine N7 atom is a major site of adduction by a large number of alkylating mutagens and carcinogens. Aflatoxin B1, a powerful mutagen, is believed to act through its reaction with this DNA site. On the basis of the specificity of base substitutions induced by various adduct forms of aflatoxin, we have proposed that bulky guanine N7 adducts elicit base substitutions by two mechanisms. The first mechanism is similar to that observed for a number of bulky noninstructive lesions, whereas the second mechanism invokes mispairing between N7-adducted guanine and thymine. A prediction of the mispairing hypothesis is that diverse bulky guanine N7 adducts (regardless of structural similarities with the aflatoxins) should induce predominantly G-to-A transitions. Accordingly, we have recently observed that base substitutions induced by the acridine half-mustard ICR-191 in the M13 double-stranded DNA transfection system are predominantly G:C-to-A:T transitions. Here, by transfecting ICR-191-treated M13 AB28 single-stranded DNA into Escherichia coli, we show that base substitutions are predominantly targeted to guanines. Since the N7-adducted-guanine:thymine mispairing is proposed to require N1 deprotonation promoted by the primary N7 lesion, guanine imidazole ring-opening should abolish this mispairing property, and thereby alter the specificity of mutagenesis. Here, we show that the incubation of ICR-191-treated RF DNA at pH 10.5 results in a significant reversal of the specificity of G:C-targeted substitutions such that G-to-T transversions predominated over G-to-A transitions.(ABSTRACT TRUNCATED AT 250 WORDS)

The impact of computer usage on the perceptions of hospital secretaries

This study explored the perceptions of hospital unit secretaries regarding computer usage. Specifically, six attitudinal variables: performance, resistance, interpersonal relations, satisfaction, challenge, and work overload were examined. The study had two major findings: (1) hospital unit secretaries have positive perceptions of job performance, satisfaction, and challenge as a result of using the PHAMIS computer system and (2) hospital unit secretaries do not feel resistant to the system, overloaded with work, or inclined to increase their interpersonal interaction with coworkers. These two findings might appear contradictory on the surface, but in fact are consistent with overall positive perceptions about the PHAMIS system. The study also considered the impact of two independent variables--age and number of years at work--on the responses of subjects. The analysis indicated that together these two variables explained some variations in the values of at least two of the dependent variables--resistance and challenge. The authors therefore concluded that the installation of the hospital computer system has established a favorable working environment for those whose work is affected by it. The dramatic expansion of computer systems in nonprofit institutions as well as in profit-oriented institutions has made people more familiar with computer technology. This trend can account for the overall positive perception of the unit secretaries toward the new computer system. Moreover, training programs and the support of top management for the system may also have enhanced the positive attitude of the users.

[Vitamin nutritional status of a high lung cancer risk population]

Vitamins A, C, D, (VA, VC, VE) and carotene (CAR) in plasma and riboflavin (VB2) in urine samples were measured to evaluate the nutritional status of 44 non-mining workers, 81 miners and 43 lung cancer patients in Yunnan Tin Mine. Plasma VA in these 3 groups averaged 46.6, 52.8, and 47.8 micrograms/dl, respectively, with 0, 0 and 7.2% of the individuals having levels under 20 micrograms/dl. The average levels of plasma CAR among these 3 groups were 153.6, 123.0 and 137.1 micrograms/dl. CAR contents in miners were significantly lower (P less than 0.01) than those of non-mining workers. About 1/4 of the miners and 1/6 of the lung cancer patients had values less than 80 micrograms/dl. Plasma VC among these 3 groups averaged 423, 406 and 360 micrograms/dl, respectively, with 14.0, 11.5 and 25.6% of the individuals having levels under 300 micrograms/dl. The average plasma VE contents ranged from 648.3 to 722.0 micrograms/dl for the 3 groups. 70.5% of non-mining workers. 42.0% of miners and 39.5% of the lung cancer patients had levels less than 700 micrograms/dl, which is considered either low or deficient in nutritional surveys. 52.3% of the non-mining workers and 51.8% of the miners were either low or deficient in VB2. Although there was intermittent supplementation of riboflavin in lung cancer patients, the low and deficient VB2 nutritional status was still observed in 27.9% of them. The study establishes the low nutritional status in vitamins of the high lung cancer risk population in Yunnan Tin Mine and provides a background for a nutritional intervention trial to prevent lung cancer in the miners.

Genetic requirements for frameshift reversion induced by bulky DNA adducts in M13 DNA

In order to analyze the genetic requirements and mechanisms of frameshift mutagenesis by activated aflatoxin B1 (AFB1), in vitro-modified phage M13 replicative form (RF) DNA was transfected into appropriate Escherichia coli cells and +1 or -1 frameshift revertants in the lacZ(alpha) gene were isolated. This analysis shows that both +1 and -1 frameshift mutagenesis by AFB1 is significantly reduced in a umuC- background. On the other hand, in the absence of RecA, +1 frameshift mutagenesis is partially reduced, but -1 frameshift mutagenesis is unaffected. DNA sequence analysis of +1 frameshifts induced by AFB1 in recA- cells suggests that the mutations occur at the same sites as in recA+ cells, but that there are significant differences in the specificity of the observed base changes. A model consistent with the observed effects in the absence of RecA suggests that an appreciable fraction of AFB1-adducted guanines can correctly template for a cytosine.

Induction of G.C to A.T transitions by the acridine half-mustard ICR-191 supports a mispairing mechanism for mutagenesis by some bulky mutagens

As the most nucleophilic atom in DNA, the guanine N7 atom is a major site of attack for a large number of chemical mutagens as well as chemotherapeutic agents. Paradoxically, while methylation of guanine N7 is believed to be largely nonmutagenic, aflatoxin B1, among the most potent mutagens, appears to exert its mutagenic activity through adduction at this site. On the basis of an analysis of the specificity of mutations induced by various adduct forms of aflatoxin B1, we have previously proposed mechanisms that can both resolve the paradox and account for the specificity of mutagenesis by aflatoxin B1. The hypothesized mechanisms specify how a bulky guanine N7 lesion can promote G.C to A.T transitions as well as frame-shift mutations. Since the proposed mechanisms are in principle lesion-independent, a simple test of the proposed mechanisms would be to examine the specificity of mutations induced by a structurally different bulky guanine N7 adduct. Toward this goal, M13 replicative form DNA was subjected to in vitro adduction with the acridine mutagen ICR-191 and transfected into Escherichia coli. Mutations in the LacZ(alpha) gene segments were scored and defined at the sequence level. The results show that ICR-191 adduction induces both base substitutions and frame shifts with near-equal efficiency. A clear majority of base substitutions were G.C to A.T transitions. On the other hand, unlike aflatoxin B1 which could induce both -1 and +1 frameshifts, ICR-191 appears to predominantly induce +1 frame shifts. This preference appears to arise by lesion-dependent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Charge densities of atoms of conjugated styryl ketones having activity against L1210 leukemia cells

Electron density calculations were undertaken on several atoms in a series of 3-substituted-4-phenyl-3-buten-2-ones in order to gain insight into the molecular features which affect charge densities. The results indicate that substituents at position 3 alter the electron densities of the olefinic group but have little effect on the acetyl function. The compounds were tested against L1210 cells in vitro, and the results suggest that electronic--but not steric--factors are important in affecting cytotoxicity. The most active compound was 3-phenylmethylene-2,4-pentanedione (1c) with an ED50 value of 1.06 x 10(-8) M.

Role of reversible phosphorylation of acetyl-CoA carboxylase in long-chain fatty acid synthesis

Acetyl-CoA carboxylase, the rate-limiting enzyme in the biogenesis of long-chain fatty acids, is regulated by phosphorylation and dephosphorylation. The major phosphorylation sites that affect carboxylase activity and the specific protein kinases responsible for phosphorylation of different sites have been identified. A form of acetyl-CoA carboxylase that is independent of citrate for activity occurs in vivo. This active form of carboxylase becomes citrate-dependent upon phosphorylation under conditions of reduced lipogenesis. Therefore, phosphorylation-dephosphorylation of acetyl-CoA carboxylase is the enzyme's primary short-term regulatory mechanism; this control mechanism together with cellular metabolites such as CoA, citrate, and palmitoyl-CoA serves to fine-tune the synthesis of long-chain fatty acids under different physiological conditions.

Mechanisms of mutagenesis by a bulky DNA lesion at the guanine N7 position

In order to examine the mechanisms of mutagenesis by a bulky DNA lesion at the guanine N7 position, the replicative form DNA of phage M13AB28 (mp8 without the amber codons in phage genes) was modified in vitro with aflatoxin B1-2,3-dichloride and transfected into appropriate Escherichia coli cells. Forward mutations in the lacZ alpha-complementing gene segment were identified as light blue or colorless plaques on appropriate indicator plates, isolated, and defined by DNA sequencing. Transfection of modified DNA into uvrA-/mucAB+ cells without prior UV (SOS) induction increased mutation frequency eight-fold over untreated DNA, whereas this increase was 12-fold upon SOS induction. Transfection of modified DNA after conversion of the primary guanine-aflatoxin lesions to the stable imidazole ring-opened formamidopyrimidine-aflatoxin suggested that these lesions were nearly equally mutagenic. A majority of point mutations under all conditions affected G:C bp. Base substitutions were in the majority, but significant frameshift mutagenesis was also detected in SOS-induced cells. Both G-to-T transversions and G-to-A transitions were produced at equal efficiency and together accounted for virtually all of the base substitutions induced by the primary lesions. Point mutations occurred predominantly at predicted damage hotspots. The characteristics of base substitution and frameshift mutations, together with available information point to multiple mechanisms of mutagenesis by this class of mutagens. The data indicate that primary lesions have the properties of both a noninstructional and pseudo-instructional lesion. In addition, the sequence context appears to play a role in determining whether a frameshift or a base substitution is induced by this bulky lesion.

Effects of SOS and MucAB functions on reactivation and mutagenesis of M13 replicative form DNA bearing bulky lesions

We have previously determined the specificity of -1 frameshifts induced by aflatoxin-B1-2,3-dichloride (AFB1C12) in phage M13 double-strand replicative form (RF) DNA. The system consists of: (i) in vitro adduction of RF DNA of BK8, a lacZ + 1 frameshift derivative of phage M13mp8; (ii) transfection into unirradiated or UV-irradiated bacterial host cells; (iii) scoring and sequencing of revertants (i.e., -1 frameshifts). The previous data had shown that induction of SOS functions enhanced mutagenesis. However, this increase in mutagenesis is not accompanied by enhanced survival in a majority of the strains tested. Here, we present evidence to show that the lack of SOS reactivation is a specific property of the RF DNA system rather than a specific property of the lesion. A model mechanism based on the replicative strategy of transfected RF DNA can account for these observations. In addition, we have calculated individual Weigle mutagenesis factors at 8 major mutagen induced sites reported previously. Analysis of these data indicates that, within a restricted subset of possible mutational events (i.e., -1 frameshifts), Weigle mutagenesis is affected by both the DNA sequence environment of the mutation site as well as the repair phenotype of the cell.

[Cytogenetic studies on 3 esophageal cancer cell lines]

The cytogenetic studies on three esophageal cancer cell lines established in China were done. Thirty metaphases showing suitable chromosome length and good G-banding pattern from each of the cell lines were chosen and subjected to karyological analysis. The typical karyotypes from these cell lines were listed, and the variation of chromosome number as well as the morphological characteristics, possible sources and the incidence of the marker chromosomes were analysed. Eca 109 is the cell line first established and used extensively in China. A strictly regular karyotype pattern was found in it: the modal number of chromosomes being 63-64; the number of each type of chromosome varying between 1-5; a distal deletion of short arm of chromosome No. 1 being discernible in all metaphases, with break sites located within 1p22-1p33. Also a distal deletion of long arm of chromosome No. 4 was usually visible. There were seven marker chromosomes with high incidence. Among them, M1 marker chromosome was a large subacrocentric chromosome which was observed in the early passages of this cell line. The chromosome number of Ec 17 cell line was usually subtetraploid. In addition to the numerical variation in some of the chromosomes, six marker chromosomes were usually observed. Among them, M1 involved reciprocal translocation between chromosome No. 1 and No. 4. M3 of Ec 17 was in correspondence with M5 of Eca 109. Both were Rob (13q;14q). The chromosome number of Ec 56 was usually subtetraploid, and in addition to the numerical variation in some of the chromosomes, seven marker chromosomes were usually observed.

Malignant transformation of baby hamster lung fibroblasts induced in vitro by a new nitrosamine compound

A new nitrosamine compound, N-1-methylacetonyl-N-3-methylbutyl-nitrosamine (MAMB-NA), isolated from corn bread inoculated with moulds commonly occurring in Linxian County, a high incidence area for esophageal cancer in North China was tested for its potential carcinogenicity in vitro. Baby hamster lung fibroblasts (BHL) were treated with MAMBNA in tissue culture medium containing liver microsome preparation of Aroclor 1254 treated rat. Cell transformation was assessed by morphological changes, loss of density-dependent inhibition and unlimited growth in vitro, chromosome changes, colony formation on soft agar, growth at low serum concentration, Con A agglutinability and tumor formation after heterotransplantation into immunosuppressed newborn rats. Like the known carcinogens N-methyl-N'-nitro-N-nitroso-guanidine and diethylnitrosamine, MAMBNA was able to cause malignant transformation of cells cultured in vitro.