Acetylcholinesterase from Drosophila melanogaster. Identification of two subunits encoded by the same gene

Purified acetylcholinesterase from Drosophila melanogaster is composed of a 55 kDa and a 16 kDa noncovalently associated subunit. Cleavage of disulfide bonds reveals that two 55 kDa polypeptides are linked together in native dimeric AChE. Western blots with two antibodies directed against the N- and C-termini of the predicted AChE primary sequence show that the 55 and 16 kDa polypeptides originate from proteolysis of the same precursor encoded by the Ace locus.     

The R-banding pattern of the Chinese hamster Don cell line

Chinese hamster cells (Don line) were treated in vivo with 5-BrdU and 33258-Hoechst fluorochrome for obtaining the partial inhibition of condensation that causes the R-banding pattern. Untreated chromosomes were stained by a standard G-banding method. Statistical measurements show significant differences in the band numbers between the two treatments. The Don cell line in the authors' laboratory presents some karyotypical differences from Don cell lines studied by other authors.     

The relation between the variability of polygenic morphological and monogenic biochemical traits as exemplified by Karakul sheep

A quantitative method for investigation of relationship between polygenic and monogenic traits has been proposed. It is based on examination of relationship between frequencies of distribution classes of an adaptive quantitative trait and frequencies of certain genetic character in the same classes. The method permits to locate a gene marker within a space of quantitative trait values. Using adaptively significant morpho-anatomic traits, it is possible to estimate indirectly adaptive values of gene markers under consideration, since, in accordance with the concept of adaptive norm, "average" phenotypes have maximal fitness, whereas deviative phenotypes transgress the bounds of the optimum. As a genetical character, genotype of certain biochemical locus, individual heterozygosity range or interlocus combinations of alleles could be used. The method has been applied to newborn Astrakhan lambs. Principal component analysis has been used to obtain complex characterization for six constitutional characters. Some regularities in location of homo- and heterozygous genotypes of the transferrin locus within a space of morphological characters' values have been revealed.     

Frequencies of chromosomal aberrations induced in human blood lymphocytes by low doses of X-rays

The dose-response for radiation-induced chromosome aberrations in human lymphocytes is usually fitted to the quadratic model. This assumes that the slope is essentially linear at low doses. Empirical observations of linearity at less than 200 mGy are, however, sparse. Some data have been published indicating a non-linear (threshold) response and these are reviewed. In particular one study with X-rays showed a plateau in response up to 50 mGy and with a significant dip below the control level at 4 mGy. The mechanism proposed to explain non-linearity is that low doses stimulate the enzymic repair capability of lymphocytes. Preliminary data are presented from a large experiment by six laboratories in which the low dose-response for X-rays has been re-examined. The plateau in the dose-response relationship, if it exists, does not extend to doses above approximately 10 mGy. No irradiated cells yielded aberration levels significantly below the control. Over the range 0-300 mGy the response can be fitted to a linear regression. There are, however, variations in sensitivity between cells from different donors. An unexpected finding was that some lymphocytes contained greater than 1 exchange aberrations. This may indicate a small subset of cells that are especially susceptible to the induction of aberrations by low doses.     

Evaluation of the risk in autosomal dominant diseases

A lot of traps and difficulties complicate the estimation of a genetic risk in the autosomal dominant diseases. The authors recapitulate the notions of mutation, penetrance and variability and illustrate by some examples the part of each of them, isolated or associated together. The increasing of molecular biology allows to resolve some of these problems, but generate new dangers which are analysed and illustrated.     

Salivary hormones: a new aspect of oral physiology

Aside from the digestive enzymes the submandibular salivary glands (SSG) synthetize other polypeptides, detected also in saliva, with varied biological activity; NGF and EGF are the knowest. However, over the last decade, steroids hormones have been also found out in the saliva at the same concentrations that the free plasma fraction. The origin of these hormones is largely discussed and certain authors have even proposed a local synthesis for them. This matter, is of clinical interest because gingiva and buccal tissues are knowingly sensitive to steroids. Besides, woman ovulation appears to be monitored through progesterone fluctuations in saliva. Another kind of salivary substances is formed by the neuropeptides of the gut-brain axis, mainly VIP and SRIF. The former likely of nervous origin seems to be involved in the atropine-resistant salivary secretion, whereas the latter-likely of SSG origin--appears as a factor associated with glycemia control.     

Thyroid function and trisomy 21. TSH increase and rT3 deficiency

An excess of thyrotropin (TSH) with normal levels of tetraiodothyronine (T4) and of 3,5,3'-triiodothyronine (T3) was confirmed in the serum of 78 trisomy 21 children. A severe deficiency of 3,3',5'-triiodo-thyronine (rT3 or reverse T3) was observed and the decrease of the rT3/TSH ratio was highly significant. These new facts suggest that the rT3 deficiency plays a peculiar role in trisomy 21 (maybe through the regulation of one or few steps of monocarbons' metabolism). A systematic control of thyroid function (including the patient's rT3 level) is mandatory for the follow-up of every trisomy 21 patient.     

Multiple binding of bilirubin to human serum albumin and cobinding with laurate

Numerical analysis of multiple binding of two ligands to one carrier has been accomplished, using the principle of several sets of acceptable binding constants, with bilirubin-laurate-albumin as an example. Binding of bilirubin to defatted human serum albumin was investigated by a spectroscopic method, based upon a difference of light absorption spectrum for free and bound bilirubin. The observations were supplemented with previous data from an independent technique, measurement of oxidation rates of free bilirubin with hydrogen peroxide and peroxidase. A continuous isotherm was obtained, showing binding of at least 4 mol bilirubin per mole albumin with the following stoichiometric binding constants, 1.11 X 10(8), 1.7 X 10(7), 8 X 10(5), and 4 X 10(4) M-1 at pH 8.2, ionic strength 0.15 M, 25 degrees C. The binding is anticooperative at all steps. A saturation level was not reached. Cobinding of bilirubin and laurate was studied, with up to 2 mol of each ligand per mole albumin, using the peroxidase method for determination of free equilibrium concentrations of bilirubin, and a dialysis rate technique for free laurate. The findings could be described in terms of a stoichiometric model. Heterotropic cooperativity was present among the first bilirubin and the first and second laurate molecules. More than two molecules of either ligand can be bound at the same time.