Relations between synthesis of deoxyribonucleotides and DNA replication in 3T6 fibroblasts

In exponentially growing 3T6 cells, the synthesis of deoxythymidine triphosphate (dTTP) is balanced by its utilization for DNA replication, with a turnover of the dTTP pool of around 5 min. We now investigate the effects of two inhibitors of DNA synthesis (aphidicolin and hydroxyurea) on the synthesis and degradation of pyrimidine deoxynucleoside triphosphates (dNTPs). Complete inhibition of DNA replication with aphidicolin did not decrease the turnover of pyrimidine dNTP pools labeled from the corresponding [3H]deoxynucleosides, only partially inhibited the in situ activity of thymidylate synthetase and resulted in excretion into the medium of thymidine derived from breakdown of dTTP synthesized de novo. These data demonstrate continued synthesis of dTTP in the absence of DNA replication. In contrast, hydroxyurea decreased the turnover of pyrimidine dNTP pools 5-50-fold. Hydroxyurea is an inhibitor of ribonucleotide reductase and stops DNA synthesis by depleting cells of purine dNTPs but not pyrimidine dNTPs. Our results suggest that degradation of dNTPs is turned off by an unknown mechanism when de novo synthesis is blocked.     

Ethoxyformylation of histidine residues in equine growth hormone

Reactivity of histidine residues in equine growth hormone to ethoxyformic anhydride was studied. The existence of two kinetically different sets was demonstrated: one of them including only the slow reacting histidine 169 (k = 0.164 min-1) and the other containing fast reacting histidines 19 and 21 (k = 0.892 min-1). A correlation between the decrease in the capacity to compete with 125I-labeled hormone for rat liver binding sites and the degree of ethoxyformylation of the fast group was found. Circular dichroism studies indicated no significant conformational changes in the protein with all three residues modified. These results fully agree with those obtained for bovine growth hormone which is further evidence supporting the vinculation of histidines 19 and/or 21 with the binding site of these hormones to their specific receptors.     

An overview of some mechanisms of bacterial pathogenesis

The adherence of microorganisms to host surfaces is highly specific, and in many cases, essential for subsequent pathogenetic events to occur. A dynamic process leading to increased mucosal adherence of gram-negative bacilli to epithelial cell receptors in the oral cavity appears to be the initial step in the development of pneumonia. In infectious processes secondary to Streptococcus pneumoniae, adherence may also play a role in specific syndromes. In many cases, however, colonization of oropharyngeal mucus itself, the presence of capsular polysaccharide, and the release of various cell wall components appear to interact to cause clinical disease. In Neisseria gonorrhoeae infections, adherence is all important and is mediated by a number of cell surface structures. These have been studied extensively. Many of these structures, such as pili and protein II, exhibit great variability both between strains and in the same organism at different stages of infection. Others, such as protein I, are more constant. This information has been used in the production of specific vaccines to more preserved structures to inhibit adherence. These will be tested in the near future. It is our view that a better understanding of the many forms of bacterial adherence will be the key to our designing more effective strategies to detect early infection and to intervene more decisively to limit its spread.     

A metabolic switch produced by enzymically interconvertible forms of an enzyme

A system of enzymically interconvertible enzyme forms (interconversion cycle) is known to increase the sensitivity to regulators. Here it is shown that this system may also provide a discrete switching mechanism in which the response is maintained when the stimulus is removed. These switches may be important in producing discontinuous metabolic changes such as those associated with cell differentiation.     

Maximal oxygen uptake in Danish adolescents 16-19 years of age

A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.