Acta biochimica et biophysica; Academiae Scientiarum Hungaricae最新文献

Fluorescamine-labelled human fibrinogen was degraded with trypsin. Using fluorescence detection, the degradation products were fractionated by Sephadex G 50 gel filtration. Fragments of 3000-10 000 molecular weight were isolated for the fluorescence polarization studies. Specific antifibrinogen antibody increased the polarization of the isolated low molecular weight fragments. These results suggest that even the smallest proteolytic fragments of fibrinogen contain antigen determinant sequences. The fluorescence polarization method offers a sensitive and valuable approach for the analysis of the small antigenic peptides of human fibrinogen.

Interaction of DNA with 1,2-5,6-dianhydro-galactitol (DAG, NSC 132 313), a bifunctional alkylating agent used in cancer therapy was studied. Treatment of lambda phage DNA with DAG in vitro protected some of the specific cleavage sites against the restriction enzyme BspI. The extent of protection depended on the concentration and time of DAG treatment but complete protection was not observed. Since the inactivation of the enzyme by DAG was excluded experimentally, the protection can be attributed to the binding of DAG to GGCC sequences of DNA. These experiments support the finding that guanine is the target of DNA alkylation by DAG (Institóris and Tamás, 1980). DAG treatment in vitro induced single strand breaks on DNA and this effect was also found to be concentration and time dependent.

It was shown in experiments made on natural actomyosin of rabbit skeletal muscle that ADP possesses direct and indirect effects on superprecipitation. The presence of ADP increases the turbidity of the actomyosin suspension. An optimal ATP/ADP ratio may help the development and existence of a PC conformer of actomyosin corresponding to a myosin-ADP-actin-myosin-ATP complex. In this complex the extent of actin-activation is controlled by the cooperativity between the two myosin heads which, on the other side, may regulate in vivo the optimal transformation of the chemical energy of ATP for mechanical work.

Fluorescein diacetate and propidium iodide double fluorescence labeling of animal sperm cells in combination with 55 degrees C treatment for 15 min was used to monitor the viability and heat tolerance of sperm cells by flow cytometry. The applicability of the elaborated test to detect fertility differences has been shown on sperm samples obtained from bulls of known fertility values. According to preliminary examinations the method seems to be suitable to test the fertility of other male animals, too. The simplicity of the relatively quick procedure may provide a new screening method to qualify male animals before using their semen for large scale artificial insemination.

The rate of 42K influx was investigated at various external sodium and ouabain concentrations in human red blood cells. In agreement with earlier reports, in red blood cells not treated with ouabain, Na did not affect K influx when [K]0 was 5.0 mM while it reduced the influx at [K]0 = 0.15 mM. However, Na stimulated 42K influx at both 5.0 mM and 0.15 mM in cells treated with ouabain (1 X 10(-5) M). When external Na concentration was raised from 0 to 72 mM the rate of 42K influx increased at [K]0 = 0.15 mM and at ouabain = 1 X 10(-5) M. The effect of external Na at different ouabain concentrations showed that K influx was inhibited by Na without or with ouabain in less than 5 X 10(-6) M while an increased K influx could be observed with higher ouabain concentrations in the incubation media. The results suggest that in the case of the complete inhibition of ouabain-sensitive K influx the electrochemical gradient of the Na ions may serve as a driving force for the inward movement of potassium.

The fast component of the electrical signal and the light absorption signals at different resolution times (at lambda = 408 nm) in an untreated purple membrane suspension were measured in order to study the stability of purple membrane fragments. It has been established that there is no change in the rate constants of L----M and M----O transitions of the photocycle in either the electrical or the light absorption signals of purple membrane suspension kept at 4 degrees C for up to 40 days. Moreover, also the amplitudes of the I (negative) and II (positive) components of the electrical signal remained unchanged during this period.

The discrete nature of the photoelectric emission cannot be neglected at low reading levels. The effect of A/D conversion after photomultiplication were both calculated and measured. The reading and its standard deviation were considerably different from those expected on the basis of a simple Poisson distribution and this should be taken into account at low reading levels. The authors describe a simple method which permits the experimental determination of photoelectron/digit conversion factor necessary for the prediction of the variation coefficient of TL measurements.