The process of lymphocyte activation in vitro can be divided into four distinct steps three of which are mitogen-dependent and the fourth is mitogen-independent. The first step is attachment of the mitogens to the cell membrane. The second step is activation of resting lymphocytes by reaction with activating receptor system. During these two phases the cells become preactivated. The third step is determination of lymphocyte response. In the fourth step the cells proceed to the S phase and eventually they may clivide, regardless of the presence or absence of mitogen. In this review I describe about important things which are required during the mitogen-dependent steps (Carbohydrate hinding specificities of mitogenic lectins, natures of receptor sites of lymphocyte cell surface for mitogenic lectins, changes of plasma membrane after binding of mitogenic lectins to lymphocyte cell surface, and kinetics of lymphocyte stimulation by mitogenic lectins).
Recent molecular orbital studies on biologically important molecules were reviewed. The topics selected were ab-initio molecular orbital studies on histamine, ascorbic acid, and morphine in relation to their physico-chemical properties as well as their biological functions. In these researches, total energies of these molecules in various conformations were calculated in order to determine the most stable conformation, and the experimental data of photoelectron spectroscopy. Furthermore, the electron distributions of these molecules were calculated to illustrate the chemical reactivities of these molecules in vivo. Another topic is semi-empirical molecular orbital studies on enzymic reaction mechanism, that is, the reaction mechanism of α-chymotrypsin was studied to determined the potential curve and the reaction path. Moreover, the theoretical approach to the catalytic action of the enzyme in terms of molecular orbital mixing was introduced with the example of the application to carboxypeptidase.
The initial stage of the interaction between HVJ virions and cells is reviewed focusing on the membrane fusion phenomenon of JVJ envelope and cell membrane. The viral protein responsible for the membrane fusion has been identified as the F glycoprotein which forms F spikes on the surface of the virion. The fusing activity of the F spike is activated by a post-translational cleavage of the F glycoprotein. The virion has a second kind of glycoprotein, HANA, which forms HANA spikes. The HANA spike possesses tow opposite activities; one is hemagglutinating activity which reflects the ability of the virus to attach the receptor, and the other is neuraminidase activity by which the virus destroys the receptor. The initial interaction between HVJ virious and cells has been intensively studied using a simplified system consisting of HVJ and red blood cells. The viral envelope comes into close contact with the celle membrane by the binding of several hundred HANA spikes on the virion envelope with the receptors on the cell membrane. Subsequently, morphological dissolution of both the viral envelope and cell membrane occurs in some parts of the region of virus-cell contact. This dissolution has been attributed to the reaction of the F spikes with the cell membrane. Immediate fusion of the virus envelope with the cell membrane then takes place. Thus the dissolved area is sealed with the virus envelope and no leakage of hemoglobin or K+ is detected throughout these virus-cell interactions. However, if viral envelope has been made permeable by freezing and thawing, immune-virolysis or heat, ion leakage occurs after envelopemembrane fusion and hemolysis follows. The F and HANA spikes integrated into cell membrane by virus-cell fusion retain their activities and can cause the cell to fuse with the other cells. Subsequently virus-cell fusion and cell-cell fusion cease as a result of the destruction of cell receptors by the neuraminidase activity of the HANA spikes.
The spin-label study on erythrocyte membrane revealed that there was heterogeneity in the fluidity in the membrane. Preservation of the heterogeneity was discussed in relation to the asymmetric distribution of phospholipids in the membrane and transmembrane linkage. It is suggested that the membrane inner proteins, such as spectrin and actin, let the membrane preserve the heterogeneity in the fluidity through the interaction with the membrane intrinsic glycoproteins, such as glycophorin and Band 3. Biological significance of the protein control of membrane structure was discussed in complementmediated hemolysis and membrane fusion by HVJ or CaF2.
Properties of various transfection systems in E. coli have been surveyed. The recipient preparations include various spheroplasts (induced by lysozyme, penicillin, or glycine), plasmolyzed or osmotically-shocked cells, cell-envelope mutants, helper-infected bacteria, frozen-thawed cells and bacteria treated with Ca2+ or Ba2+. Efficiency of transfection depends on structure of nucleic acids as well as on competence of recipients. Thus, spheroplasts preferentially take up single-stranded nucleic acids, whereas Ca2+- or Ba2+-treated cells exhibit higher efficiency for double-stranded DNA. Unlike intact phages, free nucleic acids are sensitive to cellular nucleases even after uptake, and this sensitivity is also determined by structure of the infecting molecule (strandedness, circularity etc.). Mechanism of polynucleotide uptake into cytoplasm is quite obscure as yet. Although experimental evidence is lacking, it seems not improbable that nucleic acid penetrates a proteinous channel (or pore) rather than phospholipid layer. The Ca2+- or Ba2+-dependent uptake of DNA occurs very rapidly at low temperature and extremely sensitive to phosphate. Based on peculiar cryophilic property, an involvement of lipid crystallization has been postulated in this system. Such lipid crystallization might cause conformational change of protein pore to allow penetration of nucleic acid. Structure of the putative pore may be modulated by arrangement of lipopolysaccharides and other membrane proteins. Neutralization of negative charge on cell envelope is probably another effect of Ca2+ or Ba2+.
Postsynaptic potentials of the protrusive and retractive motoneurons (P-Mn and R-Mn) in the hypoglossal motor nucleus evoked by stimulation of the bilateral lingual nerves (ipsi-L and contra-L) were explored in anesthetized cat. IPSPs in the Type B neurons of both the P-Mn and R-Mn were composed of the fast and slow IPSPs. Strychnine blocked the fast IPSP but slow IPSP was resistant to the drug. When Cl ions injected into the Mn the fast IPSP was reversed, but the slow IPSP was not. Passing the HP currents across the membrane the fast IPSP reversed to the depolarizing potentials, however, there was no changes in the slow IPSP. It was found that the ipsi-L mainly connected on the R-Mn with the synapse related to the fast IPSP, but the contra-L mainly with the synapse of the slow IPSP. From the changes of a ratio of the slow IPSP to the fast IPSP in axotomized Mns, it is suggested that the inhibitory synapses related to the slow IPSP become to diminish their effectiveness after axotomy.