The secondary structure of amides of adenylic acid containing D- and L-aromatic amino acids

Adenylyl-(5'leads to N)-amino acids containing as amino components, methyl esters of D-, L- and DL-phenylalanine, D-, L- and DL-tyrosine, and D-, L- and DL-tryptophan have been investigated by proton magnetic resonance (PMR) spectroscopy and circular dichroism (CD). The temperature and pD dependences of proton chemical shifts of these compounds have been studied. These data, together with the magnitudes of the upfield chemical shifts of the PMR signals of adenine and aromatic amino acids residues in adenylyl-(5'leads to N)-amino acids, have enabled us to construct conformational models of these compounds. The proposed conformation has been substantiated by the CD results. It is shown that in adenylyl-(5'leads to N)-amino acids the planes of adenine and amino acid aromatic moieties are roughly parallel. The aromatic rings of phenylalanine and tyrosine are localized approximately above the centre of adenine. In adenylyl-(5'leads to N)-D, -(L)-tryptophan, the six-membered rings of the indole overlaps the five-membraned ring of adenine indole partially overlaps the six-membered ring of adenine. A difference in the non-covalent interactions of D- and L-amino acids with nucleotides has been revealed. The mutual localization of the aromatic systems of AMP and the amino acids and also the positions of -OCH3 group with respect to the centre of the amino acid aromatic moiety differs in the series of the studied nucleotide derivatives of D- and L-amino acids.     

Hydrogen-induced microelectronic capacitor failure in pacemakers

Ceramic chip capacitors used in hybrid microelectronics for cardiac pacemakers are usually highly reliable. However, under certain conditions of capacitor construction, capacitor materials, mounting techniques, and environmental conditions, high failure rates may occur. A specific example is presented in which a ceramic capacitor used in an implanted pacemaker delaminated and failed approximately 30 days after being implanted. The failed capacitor caused a pulse rate rise, but due to circuit design techniques, the rate increase was limited to an acceptable value. The capacitor that failed was from an isolated lot of capacitors that was manufactured using pure palladium plates. The circuit containing this capacitor was hermetically sealed within a titanium case by welding. During the welding, a small amount of hydrogen was released from the titanium which, over a period of 2 to 4 weeks, was absorbed by the palladium plates in the capacitor. By absorbing the hydrogen, the palladium plates exhibit a volumetric expansion of sufficient magnitude to crack and delaminate the capacitor to the point of failure. Subsequently, the recurrence of this failure mode has been avoided by using capacitors containing special palladium alloys that cannot absorb hydrogen. This phenomenon is of interest to pacemaker designers since mercury batteries used in conventional pacemakers generate large amounts of hydrogen and potentially may be responsible for complications when used in conjunction with capacitors containing palladium.     

A new HLA antigen apparently not controlled by the known HLA loci

The human allogeneic serum RM3 recognizes a lymphocyte structure inherited with the HLA chromosome. Population studies show several positive associations with antigens of the HLA-A and HLA-B series. Negative association have been found with antigens of the HLA-C series. Moreover the distribution of the RM3 factor is in Hardy-Weinberg equilibrium with that of the HLA-C alleles. However, serological investigations (namely the 'lysostrip' technique) bring evidence that RM3 serum does not appear to contain antibodies directed against any of the antigens of the HLA-A, B and C series. The study of a segregant family, showing a crossing over between the HLA-A and HLA-B loci, shows that the RM3 factor segregates on the side of the HLA-A locus. In conclusion, within the limits of the serological approach used, the present study presents evidence of a new serologically defined HLA locus, different from those so far described.     

Initial studies on the penetration of spirohydantoin mustard into the cerebrospinal fluid of dogs

The possible correlations between unipolar endocardial electrogram amplitudes and voltage threshold stimulation were tested with electrodes having metallic tips of two different areas. The threshold measurements were always studied with the same pulse characteristics. The data were analyzed through five mathematical functions (linear, exponential, potential, hyperbola and translate hyperbola). The results show a significant correlation, mainly by hyperbolic and exponential functions. Consequently, we could deduce a parameter value since we already knew the other one. This was possible not only during the first implantation, but also later on.     

Ethanol potentiation of central nervous system trauma

Two models have been used to study the effects of ethanol on injuries of the central nervous system. The spinal cords of cats were injured by delivering a 200 gm-cm impact to the exposed dura mater. A second group of animals received a similar injury to the exposed dura mater overlying the cerebral hemispheres. The animals were divided into two groups, those that received an infusion of ethanol before injury, and control animals that received no ethanol. The parameters of injury used in this model produced small and insignificant lesions in those animals that received no ethanol; however, when the animals were pretreated with ethanol, a considerable increase in the extent of the injury was noted. These include alterations in membranes-bound enzymes and clotting mechanisms, and alteration of cell membranes through abnormal free radical reactions.     

Detection and estimation of azomethane in expired air of 1,2-dimethylhydrazine-treated rats

Azomethane (AM) gas was identified as a major metabolite of 1,2-dimethylhydrazine (1,2-DMH) in the expired air of F344 rats. The compound was characterized by high-pressure liquid chromatography, gas chromatography, and mass spectrometry, in comparison to a synthetic standard. At a dose of 21 mg 1,2-DMH/kg sc, approximately 14 and 11% of the dose were exhaled as AM and CO2, respectively, in 24 hours. At 200 mg 1,2-DMH/kg, 23 and 4% of the dose appeared as AM and CO2, respectively, in the respired air within the same period. Most AM was seen in the first 6 hours, but the CO2 evolution was more progressive, especially after the higher dose of 1,2-DMH.