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The coping capacity of the children during dental care depends on different factors such as age, cognitive development, personal history and social background. A good knowledge and understanding of child developmental stages will help the dentist to treat them successfully. Parental presence during treatment has been largely discussed in pediatrics and pediatric dentistry. Dentists often let parents stay in the office during the first consultation but prefer them to be in the waiting room during treatment. Depending on the case, parental presence may be needed, essential, or advised against. Parental presence during child treatment must be analyzed, but the ultimate decision is the dentist's.

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Simple rules for constructing a two-dimensional representation of relative orientations of alpha-helix residues are presented. The repeat units in tropomyosin and haemagglutinin, together with their interrelationships, are also illustrated.

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Incubation of purified human beta 2-microglobulin (B2-m) with tissue transglutaminase (Tgase) resulted in the formation of high molecular weight polymers revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In the presence of 30 mM [14C]methylamine, the polymer formation was prevented, but incorporation of methylamine into beta 2-m (equal to 1 methylamine per 1 molecule) could be observed. From the sheddings of peripheral blood mononuclear cells occurring in the presence of Tgase, it is apparent that anti-beta 2-m immunoadsorbent removed, in addition to human leukocyte antigen (HLA) and beta 2-m, some other proteins. The enzyme could incorporate [14C]methylamine into beta 2-m of the shedding cells. On addition of rabbit anti-human beta 2-m antibody, followed by fluoresceine-labeled goat anti-rabbit IgG antibody to human mononuclear blood cells, the otherwise homogeneous distribution of fluorescence turned into spots and patches on cells previously incubated with Tgase or Ca2+-ionophore A23187.

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The relative cytotoxic sensitivity of the YPC-1 tumor target cells from untreated mice and from animals treated with nitrosoureas was determined. The amount of 51Cr released from target cells increased significantly when the cells were obtained from treated mice. On the basis of the results of cold-target cytotoxicity inhibition assay, this enhancement was shown to be haplotype specific. The amount of 51Cr released from target cells of mice treated with N,N'-bis(chloroethyl)-N-nitrosourea decreased significantly when the tumor cells were first incubated with fibrinogen and transglutaminase. Based on these results and other published data, a model system is suggested. The model is based on the observation that tumors, and thus tumor antigens, at the cell surface are partly or completely covered by fibrinogen or fibrin. The enzyme transglutaminase is involved in the binding of the fibrinogen or fibrin to the cell surface. Accordingly, it is hypothesized that the nitrosoureas have a dual mode of immunotherapeutic activity. The carbamoylating properties inhibit the fibrin-binding activity of transglutaminase, thus preventing fibrin from covering up or coating the tumor cells and preventing the ability of sensitized effector cells to recognize the tumor-specific antigens in association with self H-2 antigens. The alkylating property of the nitrosoureas mainly concerns reactivity with the DNA of the tumor cells.

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A new hypothesis is presented to explain the mechanism of non-rejection of a natural allograft: the mammalian fetus during early development. Using the rabbit as a model, it is proposed here that uteroglobin (UG., MW. 15,800) synthesized in the uterus during early pregnancy, crosslinks with beta 2-microglobulin (part of the H-2 and HL-A antigens) on the embryonic cell surface. This crosslinking is achieved by the enzyme transglutaminase (coagulation factor XIIIa), which has a 4--5 fold increased activity in the uterus during early pregnancy. The conversion of pre-uteroglobin (Pre-UG) to uteroglobin (UG) and pro-transglutaminase (factor XIII) to active transglutaminase (factor XIIIa) is achieved by the concurrent increased activity of proteases present in the uterus at this time. UG is a dimeric protein with two alpha-helices running in parallel and connected by two disulfide bonds. We propose that UG molecules crosslink with beta 2-microglobulin in the presence of transglutaminase (factor XIIIa). A crosslinked beta 2-microglobulin-uteroglobin complex is formed which masks the H-2 or HL-A antigen of the implanting embryo. Thus, the maternal lymphocytes do not recognize the fetal cells as foreign. This mechanism may also explain the non-immunogenicity of ejaculated sperm in the uterus, as well as the non-immunogenicity of fetal cells found in the maternal circulation during pregnancy. At later stages of pregnancy, other proteins and/or hormones as well, may play a role in non-rejection of the fetus. However, the beta 2-microglobulin-uteroglobin complex masking the transplantation antigens of the embryo may be the major mechanism for immunological protection and non-rejection of the implanting embryo.

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The reaction of methylglyoxal with polypeptides is accompanied by an electron spin resonance absorption in the free radial region. Analysing the interaction of methylglyoxal with poly-L-lysine we found that methylglyoxal polymer formation is a major process in our system. The electron spin resonance signal seems to originate both from the polymer itself and its interaction with the polypeptide. Nuclear magnetic resonance measurements show that the methylglyoxal polymer interacts with the polypeptide via the NH groups of peptide bonds.

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The complete neglect of differential overlap method is used to investigate the binding of LiF, LiCl, NaF, and NaCl to N-methyl acetamide (NMA) as a model for these ions binding to a peptide moiety. The cation (formula: see text) anion interaction is shown to result in a net residual charge on NMA, which becomes less positive as the difference in electronegativity between the anion and cation of the salt present increases. A residual charge of smaller magnitude is also found on a water molecule in the analogous system cation (formula: see text) anion, which displays this same dependence.

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Stereochemical investigations carried out with the aid of molecular models show that the Schiff bases formed between methylglyoxal and the primary amino groups of the lysine side chains of proteins can bend back in such a way to the N atoms of the peptide groups that a charge transfer can occur between these groups and the oxygen atoms of the Schiff bases. Ab initio molecular orbital calculations support this finding.

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The effects of salts on protein--the causing of a shift in isoelectric point and the altering of the melting temperature--are proposed to be the result of binding to the protein peptide chain, which is considered as a one-dimensional solid. The interaction of methylglyoxal with protein and polylysine to give charge-transfer complexes and allow electrical conductivity are viewed as further support for the band structure of proteins. Calculations on protein chains resembling real proteins show that conductivity should be much less than expected for homopolypeptides.

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The immunization of rabbits with purified guinea pig liver transglutaminase resulted in the appearance of two antibody populations against the enzyme: one which reacted only with the Ca2+-enzyme complex and another which reacted with the intact as well as the Ca2+-enzyme. The Ca2+-induced confomrational change of the enzyme molecule exposes a new antigenic determinant which initiates the production of a specific antibody population. When the glutamine substrate of the enzyme was a dipeptide, the result of the interaction of the Ca2+-enzyme and its isolated specific antibody was an apparent activation of the catalytic activity. However, when protein substrates were used, an inhibition was observed. The characterization of the mechanism of the activation and the inhibition has led to the conclusion that the consequence of the interaction of Ca 2+-enzyme and its specific antibody is not only a limited steric hindrance of the active center but, besides that, a stabilization of the otherwise labile Ca2+-enzyme. The other antibody population reacts with both forms of the enzyme and its inhibitory effect, which has been observed in each assay, could be due to a prevention of the Ca2+-induced formation of the active enzyme.

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Under certain conditions actin can be split by thrombin. Actin prepared in the presence of excess Ca(++) was found to be resistant to thrombin. However, if actin was purified without added Ca(++), both G- and F- actin underwent thrombic digestion, although a considerable proportion of actin molecules remained intact. Similar results were obtained with actin (in 50% sucrose) devoid of nucleotide and divalent cations but retaining its native characteristic. The removal of tightly bound Ca(++) from actin by EDTA accelerated the thrombic splitting and made the complete fragmentation of G-actin possible. Thrombin first cleaves actin into two pieces and subsequently one of them, fragment K (molecular weight 37,000 on sodium dodecyl sulfate-polyacrylamide gel), splits further, resulting in fragments L (molecular weight 27,000) and M (molecular weight about 10,000).

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