[Thyrotoxic periodic paralysis. Report of a case]

A case of thyrotoxic periodic paralysis based on clinical grounds, laboratory data and therapeutic response as well is reported. The authors comment on the differential diagnosis with the most frequent types of periodic paralysis. The importance of a correct diagnosis and treatment as early as possible is stressed as to prevent further development of permanent paralysis due to irreversible degenerative myofibril changes as stated in literature.

[Acute necrotizing-ulcerative gingivitis in young men]

Acute necrotizing ulcerative gingivitis is a disease in which the bacilli of the flora normally found in the buccal cavity (fusiform bacilli and spirochetae) play a role. This type of gingivitis occurs relatively frequently in young men. The frequency of the disease tends to peak in the winter. We examined 72 young men between the ages of eighteen and twenty-one with acute necrotizing ulcerative gingivitis, fever and swelling of the regional lymph nodes for possible noxas. All of the individuals were smokers: approximately 3/4s of the group smoked more than 60 cigarettes per day. Roughly half of the individuals examined showed extremely poor oral hygiene or underlying psychological or physical stress at the onset of the disease. Dentitio difficilis and alcohol abuse however appeared to be less important factors. Symptomatic measures, such as mouthwash and oral hygiene, proved to be effective therapy. Diseases and disorders of internal structures of the body could not be diagnosed in any of these individuals.

Ultracentrifugation studies of yeast valyl-tRNA synthetase and of its interaction with tRNAVal

Yeast valyl-tRNA synthetase and its complexes with yeast tRNAVal were investigated by means of analytical ultracentrifugation. A molecular weight of 125 700 +/- 1500 and a sedimentation coefficient (SO 20, w) of 6.3 +/- 0.3 were found for the native enzyme. When the enzyme (3--60 muM) was mixed with its cognate tRNA, several types of complex were observed, depending on the relative amounts of the two macromolecules. In the presence of equimolecular amounts of tRNA and enzyme, a complex formed by the association of one of each molecule was observed with a sedimentation coefficient of about 7.3 S. However, for tRNA/enzyme stoichiometries lower than one, beside the 1 : 1 complex, a complex of higher molecular weight was observed, with a sedimentation coefficient of about 10.0 S which fits with the association of two valyl-tRNA synthetase molecules with one tRNA molecule. This 2 : 1 complex was predominant from tRNA/enzyme stoichiometries lower than 0.3. It dissociated into the 1 : 1 complex upon addition of monovalent salts or MgCl2, suggesting the electrostatic nature of the interaction in this association. All these association and dissociation phenomena were detected over a large range of pH (6.0--7.5) and in various buffers.

The yeast aminoacyl-tRNA synthetases. Methodology for their complete or partial purification and comparison of their relative activities under various extraction conditions

Several fractionation steps are described which can be applied to the partial purification of the 20 aminoacyl-tRNA synthetases from commercial baker's yeast. Comparative experiments performed in the presence or absence of protease inhibitors revealed that some enzymes prepared in the presence of the inhibitor exhibit much higher specific activities than the proteins extracted in the absence of the inhibitor. The methodology reported can be used for the simultaneous preparation of several pure aminoacyl-tRNA synthetases. As examples, the large scale purification of phenylalanyl-and valyl-tRNA synthetases are described.

Interpretation of tRNA-mischarging kinetics

Incorrect tRNA aminoacylation reactions are characterized by very slow reaction rates and by the fact that in most cases they are incomplete. In a previous study some of us explained the incompleteness of the correct aminoacylation reactions of tRNA, which can be encountered under certain experimental conditions (for instance low enzyme concentration or high ionic strength) by an equilibrium between the aminoacylation and the deacylation reactions [J. Bonnet and J.P. Ebel (1972) Eur. J.Biochem. 31, 335-344]. In the present report we bring evidence that the incorrect valylation of yeast tRNAfMet by yeast valyl-tRNA synthetase studied under standard experimental conditions, can also be described by a kinetic rate law including the rate equations of the aminoacylation and of the various deacylation reactions. In particular we show that the incomplete mischarging plateaus reflect the existence of an equilibrium between the valylation reaction on the one hand and the spontaneous and enzymic deacylation of valyl-tRNAfMet and the reverse of the valylation reaction on the other hand. However, when the valyl-tRNA synthetase concentration is not very high the reverse reaction of the amino-acylation does not play a predominant part in the establishment of the plateau. These interpretations have been extended to other mischarging systems: valylation of yeast tRNAPhE by yeast valyl-tRNA synthetase and mischarging of tRNAfMet and tRNA2Val from yeast by yeast phenylalanyl-tRNA synthetase. Unusual mischarging kinetics have been discussed. Furthermore, and as in correct systems, we found that during the mischarging of tRNAfMet one ATP is hydrolyzed per tRNA charged with valine. We conclude that the correct and the incorrect amino-acylation of tRNA behave kinetically in a similar way.