Human Papillomavirus type 16 (HPV 16) DNA is regularly found in around 50% of all cervical carcin... more Human Papillomavirus type 16 (HPV 16) DNA is regularly found in around 50% of all cervical carcinomas. Variants of this type have been found associated with different risks for cervical cancer development. Presence of HPV 16 variants in Colombia has not been previously reported. The aims of this study were to assess the feasibility of non-radioactive PCR-SSCP (polymerase chain reaction single-strand conformation polymorphism) analysis for determination of variability of ORF of E6, variability in the enhancer sequence of the LCR, and for establishment of the distribution of HPV 16 variants in invasive squamous cell carcinoma of the uterine cervix in Colombian women. Biopsies from 59 patients at the Instituto Nacional de Cancerología (INC) in Bogotá (Colombia) were collected. HPV detection was performed using universal primers. HPV 16 variants were detected by non-radioactive single-stranded conformational polymorphism (SSCP) analysis and direct sequencing. HPV 16 was detected in 57.6% of the tumors. The European branch was identified in 88.2% of the samples with the E-G350 class being the most prevalent variant (41.1%). The Asian-American branch was identified in 8.8% of the samples. Within this group it was possible to distinguish between c and a classes. It was not possible to determine the branch in 2.9% of the cases. A nucleotide transition (G to A) at position 7521 was the most prevalent variation (80%) found in the enhancer sequence of the LCR region. Conclusion: A non-radioactive PCR-SSCP analysis allowed us to distinguish between European and Asian-American branches of HPV 16, and to distinguish among classes in squamous cell carcinomas of the uterine cervix in Colombia. This method is an excellent alternative that can be used as a screening tool for identification of HPV 16 variants.
An accurate and precise knowledge of the amount of energy introduced into prebiotic discharge exp... more An accurate and precise knowledge of the amount of energy introduced into prebiotic discharge experiments is important to understand the relative roles of different energy sources in the synthesis of organic compounds in the primitive Earth's atmosphere and other planetary atmospheres. Two methods widely used to determine the power of spark discharges were evaluated, namely calorimetric and oscilloscopic, using a chemically inert gas. The power dissipated by the spark in argon at 500 Torr was determined to be 2.4 (+12%/_17%) J s_1 by calorimetry and 5.3 (± 15%) J s_1 by the oscilloscope. The difference between the two methods was attributed to (1) an incomplete conversion of the electric energy into heat, and (2) heat loss from the spark channel to the connecting cables through the electrodes. The latter contribution leads to an unwanted effect in the spark channel by lowering the spark product yields as the spark channel cools by mixing with surrounding air and by losing heat to the electrodes. Once the concentrations of the spark products have frozen at the freeze-out temperature, any additional loss of heat from the spark channel to the electrodes has no consequence in product yields. Therefore, neither methods accurately determines the net energy transferred to the system. With a lack of a quantitative knowledge of the amount of heat loss from the spark channel during the interval from ignition of the spark to when the freeze-out temperature is reached, it is recommended to derive the energy yields of the spark products from the mean value of the two methods with the uncertainty being their standard deviation. For the case of argon at 500 Torr, this would be 3.8 (±50%) J s_1.
Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, tow... more Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, towards ionizing radiation at the expense of the selective destruction of the chiral amino acids, alanine and aspartic acid. The present work examines the mechanism of this protection for the case of alanine. We have developed a computer model for the radiolysis of glycine, alanine and glycine-alanine mixtures in aqueous solution. It is established that this protection is due in part to the reaction of the α-radical of glycine with alanine to regenerate a more stable α-radical, according to the following reaction, $$ \cdot CH(NH_3^ + )CO_2^ - + CH_3 CH(NH_3^ + )CO_2^ - \to CH_2 (NH_3^ + )CO_2^ - + CH_3 \dot C(NH_3^ + )CO_2^ -$$ The rate constant of this reaction was estimated to be ≤104M-1s-1. The implications for this selective protection of glycine are considered for a hypothetical case in which there would be an enrichment of about 10% ofL-alanine in the primitive ocean and taking the glycine/alanine ratios obtained in CH4-and CO2- dominated atmospheres using electric discharge experiments. It is predicted that alanine would be rapidly destroyed and radioracemized in spite of the fact that the concentration of alanine is equal or significantly lower than that of glycine. Assuming that chiral amino acids were a prerequisite for the origin of life, it can be deduced that life could have appeared in a relatively short period of time unless there was a constant supply of optical amino acids from extraterrestrial sources.
We present a computer model calculation for the racemization of a possible excess of amino acids ... more We present a computer model calculation for the racemization of a possible excess of amino acids in the icy fraction of comet nuclei bring about by ionizing radiation released during the decay of26Al,40K,235U,238U and232Th. The model takes into account a total of 110 chemical reactions, of which 91 are needed to explain the radiation chemical processing of the major constituents of comet nuclei (Navarro-Gonzálezet al., 1992) and 19 are necessary to simulate the radiolysis of glycine/alanine mixtures in aqueous solutions (Navarro-Gonzálezet al., 1994 and 1996). It is predicted that an enantiomeric excess of alanine would not be destroyed by radioracemization during the decay of embedded radionuclides. Nevertheless, this enantiomeric excess could be attenuated by the formation of racemic amino acids in the interior of comet nuclei as a result of the radiation-induced polymerization of HCN.
Human Papillomavirus type 16 (HPV 16) DNA is regularly found in around 50% of all cervical carcin... more Human Papillomavirus type 16 (HPV 16) DNA is regularly found in around 50% of all cervical carcinomas. Variants of this type have been found associated with different risks for cervical cancer development. Presence of HPV 16 variants in Colombia has not been previously reported. The aims of this study were to assess the feasibility of non-radioactive PCR-SSCP (polymerase chain reaction single-strand conformation polymorphism) analysis for determination of variability of ORF of E6, variability in the enhancer sequence of the LCR, and for establishment of the distribution of HPV 16 variants in invasive squamous cell carcinoma of the uterine cervix in Colombian women. Biopsies from 59 patients at the Instituto Nacional de Cancerología (INC) in Bogotá (Colombia) were collected. HPV detection was performed using universal primers. HPV 16 variants were detected by non-radioactive single-stranded conformational polymorphism (SSCP) analysis and direct sequencing. HPV 16 was detected in 57.6% of the tumors. The European branch was identified in 88.2% of the samples with the E-G350 class being the most prevalent variant (41.1%). The Asian-American branch was identified in 8.8% of the samples. Within this group it was possible to distinguish between c and a classes. It was not possible to determine the branch in 2.9% of the cases. A nucleotide transition (G to A) at position 7521 was the most prevalent variation (80%) found in the enhancer sequence of the LCR region. Conclusion: A non-radioactive PCR-SSCP analysis allowed us to distinguish between European and Asian-American branches of HPV 16, and to distinguish among classes in squamous cell carcinomas of the uterine cervix in Colombia. This method is an excellent alternative that can be used as a screening tool for identification of HPV 16 variants.
An accurate and precise knowledge of the amount of energy introduced into prebiotic discharge exp... more An accurate and precise knowledge of the amount of energy introduced into prebiotic discharge experiments is important to understand the relative roles of different energy sources in the synthesis of organic compounds in the primitive Earth's atmosphere and other planetary atmospheres. Two methods widely used to determine the power of spark discharges were evaluated, namely calorimetric and oscilloscopic, using a chemically inert gas. The power dissipated by the spark in argon at 500 Torr was determined to be 2.4 (+12%/_17%) J s_1 by calorimetry and 5.3 (± 15%) J s_1 by the oscilloscope. The difference between the two methods was attributed to (1) an incomplete conversion of the electric energy into heat, and (2) heat loss from the spark channel to the connecting cables through the electrodes. The latter contribution leads to an unwanted effect in the spark channel by lowering the spark product yields as the spark channel cools by mixing with surrounding air and by losing heat to the electrodes. Once the concentrations of the spark products have frozen at the freeze-out temperature, any additional loss of heat from the spark channel to the electrodes has no consequence in product yields. Therefore, neither methods accurately determines the net energy transferred to the system. With a lack of a quantitative knowledge of the amount of heat loss from the spark channel during the interval from ignition of the spark to when the freeze-out temperature is reached, it is recommended to derive the energy yields of the spark products from the mean value of the two methods with the uncertainty being their standard deviation. For the case of argon at 500 Torr, this would be 3.8 (±50%) J s_1.
Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, tow... more Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, towards ionizing radiation at the expense of the selective destruction of the chiral amino acids, alanine and aspartic acid. The present work examines the mechanism of this protection for the case of alanine. We have developed a computer model for the radiolysis of glycine, alanine and glycine-alanine mixtures in aqueous solution. It is established that this protection is due in part to the reaction of the α-radical of glycine with alanine to regenerate a more stable α-radical, according to the following reaction, $$ \cdot CH(NH_3^ + )CO_2^ - + CH_3 CH(NH_3^ + )CO_2^ - \to CH_2 (NH_3^ + )CO_2^ - + CH_3 \dot C(NH_3^ + )CO_2^ -$$ The rate constant of this reaction was estimated to be ≤104M-1s-1. The implications for this selective protection of glycine are considered for a hypothetical case in which there would be an enrichment of about 10% ofL-alanine in the primitive ocean and taking the glycine/alanine ratios obtained in CH4-and CO2- dominated atmospheres using electric discharge experiments. It is predicted that alanine would be rapidly destroyed and radioracemized in spite of the fact that the concentration of alanine is equal or significantly lower than that of glycine. Assuming that chiral amino acids were a prerequisite for the origin of life, it can be deduced that life could have appeared in a relatively short period of time unless there was a constant supply of optical amino acids from extraterrestrial sources.
We present a computer model calculation for the racemization of a possible excess of amino acids ... more We present a computer model calculation for the racemization of a possible excess of amino acids in the icy fraction of comet nuclei bring about by ionizing radiation released during the decay of26Al,40K,235U,238U and232Th. The model takes into account a total of 110 chemical reactions, of which 91 are needed to explain the radiation chemical processing of the major constituents of comet nuclei (Navarro-Gonzálezet al., 1992) and 19 are necessary to simulate the radiolysis of glycine/alanine mixtures in aqueous solutions (Navarro-Gonzálezet al., 1994 and 1996). It is predicted that an enantiomeric excess of alanine would not be destroyed by radioracemization during the decay of embedded radionuclides. Nevertheless, this enantiomeric excess could be attenuated by the formation of racemic amino acids in the interior of comet nuclei as a result of the radiation-induced polymerization of HCN.
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Papers by Alfredo Romero