Effect of Temperature of Liquid Nitrogen on Radiation Resistance of Spores of Clostridium botulinum

An apparatus consisting of a Dewar flask and a relay system controlling the flow of liquid nitrogen permitted the irradiation of samples in tin cans or Pyrex tubes at temperatures ranging from 0 ± 1.5 C to -194 ± 2 C. An inoculated pack comprising 320 cans of ground beef containing 5 × 10⁴ spores of Clostridium botulinum 33A per can (10 cans per radiation dose) was irradiated with Co⁶⁰ at 0 and -196 C. Incubation was carried out at 30 C for 6 months. Approximately 0.9 Mrad more radiation was required to inactivate the spores at -196 C than at 0 C. Cans irradiated at -196 C showed partial spoilage at 3.6 Mrad and no spoilage at 3.9 Mrad; the corresponding spoilage-no spoilage doses at 0 C were 2.7 and 3.0, respectively. The majority of positive cans swelled in 2 to 14 days; occasional swelling occurred as late as 20 days. At progressively higher doses, swelling was delayed proportionally to the radiation dose received. The remaining nonswollen cans had no toxin after 6 months of storage, although occasional cans contained very low numbers of viable spores comprising on the average 0.1% of the original spore inoculum. The D₁₀ values in phosphate buffer were 0.290 Mrad for 0 C and 0.396 Mrad for -196 C; in ground beef, the corresponding D₁₀ values were 0.463 Mrad and 0.680 Mrad, respectively. These D₁₀ values indicate that the lethal effect of γ rays decreased at -196 C as compared with 0 C by 13.5% in phosphate buffer, and by 47% in ground beef.     

Investigation of switch from ATM to ATR signaling at the sites of DNA damage induced by low and high LET radiation

Upon induction of DNA damage by ionizing radiation (IR), members of the phosphatidylinositol 3-kinase-like kinase family of proteins namely ataxia-telangiectasia mutated (ATM), DNA-PKcs, and ATM- and Rad3-related (ATR) maintain genomic integrity by mounting DNA damage response (DDR). Recent reports suggest that activation of ATM and ATR are oppositely regulated by the length of single stranded overhangs generated during end processing by nucleases at the break sites. These stretches of single stranded overhangs hold the clue for the transition from ATM to ATR signaling at broken DNA ends. We investigated whether differential processing of breaks induced by low and high LET radiation augments the phenomenon of switching from ATM to ATR kinase and hence a concomitant NHEJ to HR transition at the sites of DNA damage. 82-6 human fibroblasts were irradiated with 1 or 2 Gy of γ-rays and particle radiation of increasing LET in order to increase the complexity and variability of DNA double strand breaks (DSB) structures. The activation kinetics of ATM and ATR kinases along with their downstream substrates were determined utilizing Western blotting and immunofluorescence techniques. Our data provide evidence of a potential switch from ATM to ATR kinase signaling in cells treated with γ-rays at approximately 2 h post irradiation, with induction and completion of resection denoted by Rad51 foci resolution kinetics and observed with a significant decline of phosphorylated ATR kinase 8 h after IR. On the other hand, irradiation with high LET 600 MeV/u ⁵⁶Fe (180 keV/μm) and 170 MeV/u ²⁸Si (99 keV/μm) particles show a similar Rad51 foci decay kinetics, however, exhibiting prolonged resection, evident by the persistent phosphorylated ATM and ATR kinase until 24 h post irradiation. This residual effect, however, was significantly reduced for 250 MeV/u ¹⁶O particles of moderate LET (25 keV/μm) and absent for γ-rays. Hence, our results support the hypothesis that the transition from ATM to ATR signaling at DNA break sites is extended for longer periods of time, indicated by sustained resection due to the complex type of damage induced, a hallmark of high LET radiation, which may contribute to its increased biological effectiveness.     

Change in Microflora of Sewage Sludge by Gamma-ray Irradiation

Total bacteria of activated dewatered sludge cake of Takasaki city which amounted to 2 × 10⁹ per gram diminished rapidly with the radiation dose, but slowly after 0.5 Mrad, and 10³ per gram survived even after 10 Mrad irradiation. However, coliforms which amounted to 8 × 10⁷ per gram were inactivated below 0.5 Mrad irradiation. The predominant bacteria in non-irradiated sludge were Pseudomonas cepacia and it mainly survived up to 2 Mrad, but Bacillus were predominant at 0.5 to 0.7 Mrad irradiation. The main residual flora from 2 to 5 Mrad was composed of Pseudomonas soranacearum, P. cepacia and P. delafieldii, and the main residual flora in more than 5 Mrad irradiated sludge was P. flava . These typical strains of Pseudomonas in phosphate buffer were radiation sensitive, and their D₁₀ values were from 0.005 to 0.021 Mrad under aerobic irradiation conditions.     

Targeting ATR in vivo using the novel inhibitor VE-822 results in selective sensitization of pancreatic tumors to radiation

Combined radiochemotherapy is the currently used therapy for locally advanced pancreatic ductal adenocarcinoma (PDAC), but normal tissue toxicity limits its application. Here we test the hypothesis that inhibition of ATR (ATM-Rad3-related) could increase the sensitivity of the cancer cells to radiation or chemotherapy without affecting normal cells. We tested VE-822, an ATR inhibitor, for in vitro and in vivo radiosensitization. Chk1 phosphorylation was used to indicate ATR activity, γH2AX and 53BP1 foci as evidence of DNA damage and Rad51 foci for homologous recombination activity. Sensitivity to radiation (XRT) and gemcitabine was measured with clonogenic assays in vitro and tumor growth delay in vivo. Murine intestinal damage was evaluated after abdominal XRT. VE-822 inhibited ATR in vitro and in vivo. VE-822 decreased maintenance of cell-cycle checkpoints, increased persistent DNA damage and decreased homologous recombination in irradiated cancer cells. VE-822 decreased survival of pancreatic cancer cells but not normal cells in response to XRT or gemcitabine. VE-822 markedly prolonged growth delay of pancreatic cancer xenografts after XRT and gemcitabine-based chemoradiation without augmenting normal cell or tissue toxicity. These findings support ATR inhibition as a promising new approach to improve the therapeutic ration of radiochemotherapy for patients with PDAC.     

Infrared absorption and raman scattering of sulfate groups of heparin and related glycosaminoglycans in aqueous solution

The i.r. spectra for aqueous solutions of sulfated glycosaminoglycans and model compounds in the transmittance “window” region of the solvent (1400-950 cm^?1) are dominated by the strong and complex absorption centered at ～1230 cm^?1 and associated with the antisymmetric stretching vibrations of the SO groups. Primary and secondary O-sulfate groups absorb at somewhat higher frequencies (1260-1200 cm^?1) than N-sulfates (～1185 cm^?1). Each sulfate band lends itself to quantitative applications, especially within a given class of sulfated polysaccharide. Laser-Raman spectra of heparin and model compounds have been obtained in aqueous solution and in the solid state. The most-prominent Raman peak (at ～1060 cm^?1) is attributable to the symmetrical vibration of the SO groups, with N-sulfates emitting at somewhat lower frequencies (～1040 cm^?1) than O-sulfates. The Raman pattern in the 950-800 cm^?1 region (currently used in the i.r. for distinguishing between types of sulfate groups) also involves vibrations that are not localized only in the COS bonds.     

Radiation Sterilization of Bacon for Military Feeding

Sliced, cured bacon, packed in cans and seeded with 6 × 10⁵ spores per can of Clostridium botulinum strains 33A or 41B, or with 3 × 10⁶ spores per can of strains 36A, 12885A, 9B, or 53B, was irradiated to various dose levels with γ radiation. Evidence provided by swelling, toxicity, and recoverable C. botulinum with 2,200 inoculated, irradiated cans demonstrated that: (i) 4.5 Mrad were more than adequate as a sterilization dose; (ii) the experimental minimal sterilizing dose was 2.0 Mrad, and the theoretical 12-log reduction dose was 2.65 or 2.87 Mrad depending on the method of calculation; (iii) some spoilage occurred at dose levels below 2.0 Mrad; (iv) all visible spoilage of irradiated bacon was due to strains 33A and 12885A only, whose D values were, respectively, 0.141 and 0.177 Mrad based on spoilage data, and 0.221 and 0.188 Mrad, respectively, when based on recovery data; (v) toxic cans did not always result in swelling, nor did swollen cans always produce toxic spoilage; and (vi) viable C. botulinum can exist for at least 8 months in storage at 30 C without producing visible or toxic spoilage at doses below 2.0 Mrad.     

Quaternary structures and low frequency molecular vibrations of haems of deoxy and oxyhaemoglobin studied by resonance Raman scattering

The influence of quaternary structure on the low frequency molecular vibrations of the haem within deoxyhaemoglobin (deoxy Hb) and Oxyhaemoglobin (oxy Hb) was studied by resonance Raman scattering. The FeO₂ stretching frequency was essentially identical between the high affinity (R) state (Hb A) and low affinity (T) state (Hb Kansas and Hb M Milwaukee with inositol hexaphosphate). However in deoxy Hb, only one of the polarized lines showed an appreciable frequency shift upon switch of quaternary structure, i.e. 215 to 218 cm^?1 for the T state (Hb A, des-His(146β) Hb, and des-Arg(141α) Hb (pH 6.5)) and 220 to 221 cm^?1 for the R state (des-Arg(141α) Hb (pH 9.0), des-His(146β)-Arg(141α) Hb and NES des-Arg(141α) Hb). Based on the observed ⁵⁴Fe isotopic frequency shift of the corresponding Raman lines of deoxy Hb A (214 → 217 cm^?1), of deoxy NES des-Arg Hb (220 → 223 cm^?1), of the protoporphyrinato-Fe(II)-(2-methylimidazole) complex in the ferrous high spin state (207 → 211 cm^?1) and of deoxymyoglobin (220 → 222 cm^?1) (Kitagawa et al., 1979), and on substitution of perdeuterated for protonated 2-methylimidazole in the deoxygenated picket fence complex (T_pivPP)Fe²⁺ (2-MeIm) (209 → 206 cm^?1), and on the results of normal co-ordinates calculation carried out previously, we proposed that the 216 cm^?1 line of deoxy Hb is associated primarily with the FeN_ε(HisF8) stretching mode and accordingly that the FeN_ε(HisF8) bond is stretched in the T state due to a strain exerted by globin.     

Molecular alterations produced in bacterial cells by ionizing radiation

Biochemical effects of high doses of 0.8 Mev electrons onEscherichia coli B were studied using infrared spectroscopy (IR). Aqueous suspensions of the bacterial cells were irradiated in open petri dishes. After exposure, films of these cells were examined for absorption of light between 4000 cm^–1 to 600 cm^–1. The qualitative aspects of the changes in the absorption spectra indicative of molecular alteration were noted and attempts were made to interpret them. The damage is selective in that some molecular groups are affected more than others. In general the changes indicate breakup of biopolymers and overall oxidation. All exposure doses given were above 1.0×10⁶ Roentgen.     

Rapid electroelution of nucleic acids from agarose and acrylamide gels

The alkaline/filter DNA elution technique measures single-strand DNA breaks in mammalian cells based on the DNA molecular weight dependent retention of the macromolecule on 2-μm-pore-size filters. Described here is a modification of the technique which uses [³H]thymidine-labeled DNA of γ-irradiated cells as an internal reference. Thus, an increased precision is obtained in the assessment of this type of DNA damage at biologically significant radiation doses (i.e., where cell survival occurs). The measure of DNA damage is based on the actual initial DNA elution rate, i.e., arithmetic ratio of the elution of “test” DNA (i.e., ¹⁴C-labeled DNA) relative to the elution of “reference” DNA (i.e., ³H-labeled DNA). The repair of this damage on postirradiation incubation of the cells is detected as a decrease in the rate of “test” DNA cluted relative to “reference” DNA from unincubated cells. For Chinese hamster V79–171 cells irradiated with 5 Gy (500 rads), repair can be resolved into two first-order processes having rate constants (at 24°C) of ～0.190 and ～0.017 min^?1.     

Respiration and metabolic processes of bacteria in autoclaved and gamma-irradiated soil

Samples of chernozem and brown soils were irradiated with gamma rays using doses of 1.5 to 4.5 Mrad, or fractionally autoclaved at 1 and 2 kp/cm². Consumption of oxygen by cellular suspensions of bacteria added to suspensions of sterilized soils was higher than in untreated samples. The increased oxygen consumption indicated an increase in the quantity of a biologically oxidizable substrate which could be released during the irradiation or autoclaving of soils. The amount of oxygen consumed was proportional to the radiation dose or autoclaving time and the pressure used, and was dependent also on the type of soil. The accessible substrate could be immediately, without a lag phase, oxidized by the added microorganism. The extent and rate of oxygen consumption in the sterilized soil samples varied in different microorganisms. It was observed that decomposition of vanillie acid by a cell suspension ofCellulomonas sp. was stimulated in the soil sterilized by radiation. The significance of these findings for the soil metabolic studies is discussed.     

Infrared absorbance spectroscopy of aqueous proteins: Comparison of transmission and ATR data collection and analysis for secondary structure fitting

Attenuated total reflectance (ATR) infrared absorbance spectroscopy of proteins in aqueous solution is much easier to perform than transmission spectroscopy, where short path‐length cells need to be assembled reproducibly. However, the shape of the resulting ATR infrared spectrum varies with the refractive index of the sample and the instrument configuration. Refractive index in turn depends on the absorbance of the sample. In this work, it is shown that a room temperature triglycine sulfate detector and a ZnSe ATR unit can be used to collect reproducible spectra of proteins. A simple method for transforming the protein ATR spectrum into the shape of the transmission spectrum is also given, which proceeds by approximating a Kramers‐Krönig–determined refractive index of water as a sum of four linear components across the amide I and II regions. The light intensity at the crystal surface (with 45° incidence) and its rate of decay away from the surface is determined as a function of the wave number–dependent refractive index as well as the decay of the evanescent wave from the surface. The result is a single correction factor at each wave number. The spectra were normalized to a maximum of 1 between 1600 cm^?1 and 1700 cm^?1 and a self‐organizing map secondary structure fitting algorithm, SOMSpec, applied using the BioTools reference set. The resulting secondary structure estimates are encouraging for the future of ATR spectroscopy for biopharmaceutical characterization and quality control applications.     

An infrared spectroscopy study of the molecular structure changes of DNA after electron and ultraviolet irradiation

Samples of calf thymus DNA and two different leukemic leukocyte DNA's in the solid state have been irradiated (at 300°K) with 800 keV electrons and 4.9 eV (2537Å) ultraviolet rays. The subsequent effects on the DNA's have been studied using infrared spectroscopy as the probe for radiation-produced molecular alterations. The region of the infrared spectrum studied covered the wave number range from 4000 cm⁻¹ to 300 cm⁻¹. Our results indicate that under electron and ultraviolet irradiation, the prominent infrared active absorption peaks of all three DNA's are altered. The infrared results of our ultraviolet irradiation of DNA indicate that similar molecular bonds are broken as for the case of DNA irradiated with 800 keV electrons. The results indicate that up to high doses, calf thymus DNA is more sensitive to electron irradiation than the leukemic leukocyte DNA's. The infrared active absorption peaks of the two leukemic leukocyte DNA's respond similarly to electrons. The ultraviolet results indicate some difference between calf thymus DNA and the two leukocyte DNA's in their response to 4.9 eV light.     

Alterations in histone acetylation following exposure to <Superscript>60</Superscript>Co γ-rays and their relationship with chromosome damage in human lymphoblastoid cells

Chromosome damage is related to DNA damage and erroneous repair. It can cause cell dysfunction and ultimately induce carcinogenesis. Histone acetylation is crucial for regulating chromatin structure and DNA damage repair. Ionizing radiation (IR) can alter histone acetylation. However, variations in histone acetylation in response to IR exposure and the relationship between histone acetylation and IR-induced chromosome damage remains unclear. Hence, this study investigated the variation in the total acetylation levels of H3 and H4 in human lymphocytes exposed to 0–2 Gy ⁶⁰Co γ-rays. Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, was added to modify the histone acetylation state of irradiated cells. Then, the total acetylation level, enzyme activity, dicentric plus centric rings (dic?+?r) frequencies, and micronucleus (MN) frequencies of the treated cells were analyzed. Results indicated that the acetylation levels of H3 and H4 significantly decreased at 1 and 24 h, respectively, after radiation exposure. The acetylation levels of H3 and H4 in irradiated groups treated with SAHA were significantly higher than those in irradiated groups that were not treated with SAHA. SAHA treatment inhibited HDAC activity in cells exposed to 0–1 Gy ⁶⁰Co γ-rays. SAHA treatment significantly decreased dic?+?r/cell and MN/cell in cells exposed to 0.5 or 1.0 Gy ⁶⁰Co γ-rays relative to that in cells that did not receive SAHA treatment. In conclusion, histone acetylation is significantly affected by IR and is involved in chromosome damage induced by ⁶⁰Co γ-radiation.     

Resonance Raman scattering and optical absorption of adrenodoxin and selena-adrenodoxin

Raman spectra have been recorded for native and selenium substituted adrenodoxin in dilute solution. Adrenodoxin shows three bands at 397, 350 and 297 cm^?1, all polarized, which can be associated with the iron-sulfur core. Selenium substitution leaves the 350 cm^?1 band essentially unshifted, but the other two bands disappear and are replaced by new bands at 355 and 263 cm^?1. The 350 cm^?1 band is assigned to stretching of iron-sulfur (cysteine) bonds, while the 397 and 297 cm^?1 bands are associated with vibrations of the labile sulfur atoms. The iron-selenium charge transfer bands were observed at 438 and 480 nm for the oxidized form and at 580 nm for the reduced form. The reduced selena-adrenodoxin displayed absorption maxima at 4, 450 and 5, 550 cm^?1, which can be assigned to the d-d transitions of high-spin ferrous ion. From this data and the reported g-values of electron paramagnetic resonance signals, the spin-orbit coupling constants were calculated to be 170 and 210 cm^?1 for the respective d-d transitions.     

Cooperative Response of Escherichia Coli Cells to the Resonance Effect of Millimeter Waves at Super Low Intensity

Cells of Escherichia coli K12 AB1157 were irradiated with millimeter waves (MMW) within the power density (PD) range of 10^?20 to 10 ⁴ W/cm². MMW were applied for 0.5–70 min at 51.76 GHz or 41.32 GHz at which, as had been shown earlier, MMW resonantly changes the genome conformational state (GCS) of E. coli K12 AB1157 cells. The changes in the GCS were tested with the method of anomalous viscosity time dependence (AVTD). It was demonstrated that the resonance effect of MMW manifests itself at PD up to 10^?19 W/cm². Dependences of MMW effect on power density and time of exposure proved to have distinct characteristics when cells are irradiated during the logarithmic or stationary phases of the culture's growth. It was found that the resonance effect of MMW on the GCS of E. coli cells at the early stationary phase changes the developmental dynamics of the irradiated culture. It was established for the first time that the magnitude of the resonance MMW effect depends on the concentration of irradiated cells. An analysis of the results indicates an electromagnetic rather than diffusion nature of the cells' cooperative responses to millimeter waves.     

Time-resolved resonance Raman spectroscopy of cytochrome c reduced by pulse radiolysis

The first investigation of the dynamics of a redox transition of an electron-transfer enzyme by time-resolved resonance Raman spectroscopy in combination with pulse-radiolytical reduction is described by an application to cytochrome c. A long-lived transient state is observed upon reduction of the alkaline form of cytochrome c as a distinct frequency shift of one resonance Raman band. From the frequency in the stable oxidized state, 1567 cm^?1, this particular resonance Raman band shifts within less than 1 μs to 1533 cm^?1 in the transient reduced state, which has a lifetime longer than 20 ms but shorter than a few seconds. Finally, in the stable reduced state, this band is located at 1547 cm^?1. According to a previous normal coordinate analysis, this resonance Raman band can be assigned predominantly to a stretching mode of the outermost C-C bonds in the four pyrrole rings of porphyrin. This vibrational mode is influenced by the protein most directly through the covalent thioether linkages of two cysteines to porphyrin. We interpret the long lifetime of the transient state as due to the slow return of Met-80 as sixth ligand to the heme iron upon reduction of the alkaline form of cytochrome c.     

Raman intensities of carbon-carbon stretching modes in a model membrane

Laser-Raman spectra of L-α-dimyristoylphosphatidylcholine (DMPC) liposomes in the spectral range 1000–1200 cm^?1 were obtained as a function of temperature from ?80 to +50°C. The triplet found in this spectral region was resolved into Lorentzian components by means of an iterative computer program. The peak intensities, band widths, and band areas of the resolved 1062 cm^?1 and 1130 cm^?1 bands, assigned to CC stretching vibrations of trans segments, were evaluated as a function of temperature. While the peak intensities of the bands decrease substantially with temperature, the band widths show a considerable increase. The change in band areas is therefore smaller than the change in peak heights. Experiments with all trans carboxylic acids showed that in these compounds the area of the Raman bands at 1062 cm^?1 and 1130 cm^?1 is proportional to the number of trans bonds. The variation with temperature of the number of trans and gauche bonds in the studied phospholipid is reflected by the change of the area of the 1130 cm^?1 Raman band.     

Lateral diffusion and patch formation of H-2Kk antigens on mouse spleen lymphocytes

We have studied the diffusion and aggregation of H-2K^k antigens labeled with a fluorescent anti-H-2K^k monoclonal antibody (IgG) on mouse splenic lymphocytes, employing fluorescence photobleaching recovery and fluorescence microscopy. The H-2K^k antigens were initially distributed homogeneously on all lymphocytes. Upon antibody binding, sub-micron patches were formed on 50–60% of the cells. A lateral diffusion coefficient, D, of 7.1·10^?10 cm²/s and a mobile fraction of 0.73 were found for H-2K^k antigens on diffusely-labeled cells, while these antigens were immobile (D?5·10^?12 cm²/s) on patched cells. The patched and nonpatched sub-populations did not correspond to B- and T-lymphocytes. Subjection to low temperature or treatment with NaN₃ or cytoskeleton-disrupting drugs did not affect the diffusion or patching of H-2K^k, indicating no involvement of metabolic energy or drug-sensitive cytoskeletal components. These findings could be related to the interactions of H-2 antigens on the cell surface, and to the different susceptibilities of various cells to lysis by cytotoxic T-cells.     

Raman studies of the crystalline, solution, and alkaline-denatured states of beta-lactoglobulin.

The Raman spectra of β-lactoglobulin in the crystalline, freeze-dried, and solution states are compared. The spectra of the freeze-dried and crystalline proteins were practically identical. The conformationally sensitive amide III line appearing at 1242 cm^?1 increased in intensity 30% upon dissolution of the protein in water which is interpreted as a conformational change in the disordered chains of the protein. This result appears to be a phenomenon for globular proteins containing a large disordered chain fraction. The alkaline denaturation of β-lactoglobulin was studied. When the pH was increased from 6.0 to 11.0, the amide III line shifted from 1242 to 1246 cm^?1, broadened, and decreased in intensity. This is consistent with the conversion of β-sheet regions in β-lactoglobulin to the disordered conformation, as has been proposed by other investigators. At pH 13.5 the amide III shifts to 1257 cm^?1 characteristic of a completely disordered protein, indicating that any remaining “core” of β-sheet has been randomized. Several changes in the intensities of the tyrosine and tryptophan vibrations accompany the denaturation. As the pH is increased from 6.0 (native state) to 11.0 (denatured state) the intensity ratio of two tyrosine ring vibrations, I₈₅₅ cm^?1/I₈₃₀ cm^?1, decreases from 1.0:0.9 to 1.0:1.3. The same ratio for a copolymer consisting of 95% glutamic acid and 5% tyrosine at pH 7.0, where the polymer forms a random coil exposing the tyrosine to the aqueous environment, is 1.0:0.62. This ratio more closely resembles that corresponding to β-lactoglobulin at pH 6.0 (native state) than pH 11.0 (denatured state) suggesting that the average tyrosine in the denatured state may be in a more hydrophobic environment than in the native state. A time-dependent polymerization of the denatured protein reported by other investigators and observed by us may account for the change in the tyrosine environment. A tryptophan vibration appearing at 833 cm^?1 in the spectrum of the native state becomes weak as the pH is increased to 11.0. The intensity of this line may also reflect the local environment of the tryptophan residue.     

Influence of MLS laser radiation on erythrocyte membrane fluidity and secondary structure of human serum albumin

The biostimulating activity of low level laser radiation of various wavelengths and energy doses is widely documented in the literature, but the mechanisms of the intracellular reactions involved are not precisely known. The aim of this paper is to evaluate the influence of low level laser radiation from an multiwave locked system (MLS) of two wavelengths (wavelength = 808 nm in continuous emission and 905 nm in pulsed emission) on the human erythrocyte membrane and on the secondary structure of human serum albumin (HSA). Human erythrocytes membranes and HSA were irradiated with laser light of low intensity with surface energy density ranging from 0.46 to 4.9 J cm^?2 and surface energy power density 195 mW cm^?2 (1,000 Hz) and 230 mW cm^?2 (2,000 Hz). Structural and functional changes in the erythrocyte membrane were characterized by its fluidity, while changes in the protein were monitored by its secondary structure. Dose-dependent changes in erythrocyte membrane fluidity were induced by near-infrared laser radiation. Slight changes in the secondary structure of HSA were also noted. MLS laser radiation influences the structure and function of the human erythrocyte membrane resulting in a change in fluidity.