Rates of peptidoglycan turnover and cell growth of Bacillus subtilis are correlated

Peptidoglycan turnover was measured by the decrease of trichloroacetic acid-precipitable label in cells labeled with N-acetyl-D-[14C]glucosamine. The rate of turnover was reduced strongly by the inhibition of RNA or protein synthesis and weakly by the inhibition of lipid, peptidoglycan, or DNA synthesis. It increased with the growth rate (which was controlled by the concentration of oxomethylvalerate limiting the intracellular isoleucine supply) to the same degree in stringent (rel+) and isogenic relaxed (relA) strains. In these and all other strains tested, the turnover rate (k) increased with the growth rate (g) according to the equation, k = 0.70 X g1.38, even when the growth rate was systematically altered by changes in the temperature or in the composition of the medium.     

Phagocytosis of hydroxyapatite or calcium pyrophosphate dihydrate crystals by rabbit articular chondrocytes stimulates release of collagenase, neutral protease, and prostaglandins E2 and F2 alpha

Synthetic hydroxyapatite (HA) and calcium pyrophosphate dihydrate (CPPD) microcrystals are phagocytosed by rabbit articular-cartilage chondrocytes in primary culture. The ingestion of crystals greatly stimulated the release of collagenase, neutral protease, and prostaglandins E2 and F2 alpha into the ambient medium. Lactate dehydrogenase was not released by either crystal despite electron microscopic evidence of cell damage by HA crystals (partial loss of phagolysosomal membrane and increased myelin figures). HA, but not CPPD crystals, stimulated release of beta-glucuronidase. HA crystal concentrations from 50 to 200 micrograms ml-1 induced a dose-dependent release of collagenase and of extracellular protein. Both phagocytosis and collagenase release were greatly attenuated when HA crystals were added to the chondrocyte monolayers in the absence of serum. As HA and CPPD crystals have been identified in human articular cartilage in association with degenerative changes, it is possible that the cell-crystal interaction described here may be pathogenetically important.     

Variations in problem conceptualizations and intended solutions among Hong Kong students

Cognitive schema were used to explain health and illness behaviors among Chinese students. University students in Hong Kong were asked to attribute causes and suggest solutions to five health/mental health problems: Weakness/Fatigue, Tension/ Anxiety, Sleep Difficulty, Hollow/Emptiness, and Headache. The patterns of endorsement on the causal and solution categories used for the five problems were compared using a new asymptotic chi-squared test. The response patterns were found to be significantly different across the five problems. Each problem was attributed to multiple causes including psychological, social, situational, somatic, and existential factors. The intended solutions were often related to the nature of the causal attributions especially when the problems were mild. In lay help-seeking, the Hong Kong students would attempt a variety of self-help measures. However, for professional consultation, the medical doctor would be the primary care professional the students would turn to for most of the problems except in the case of Hollow/Emptiness.     

Calmodulin-dependent protein phosphatase: a developmental study

Calmodulin-dependent protein phosphatase, one of the major calmodulin-binding proteins in bovine brain, dephosphorylates casein with a specific activity of 15 nmol mg-1 min-1 at 30 degrees C. The stimulation of phosphatase activity by calmodulin is reversed by ethylene glycol bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid or trifluoperazine, a calmodulin antagonist. Antibodies raised in rabbit against the phosphatase inhibit the enzyme activity. The levels of the protein in brain extracts from various animals, determined by a radioimmunoassay, range from 20 micrograms/g of tissue in chick and fish brains to 143 micrograms in rat cerebrum. The ontogeny of the phosphatase was studied in nervous tissues from rat and chick, animals in which synaptogenesis takes place at different times during their development. The levels of the protein increased significantly in rat cerebrum and cerebellum and in chick brain and retina during the periods corresponding to major synapse formation. In rat cerebrum, the enzyme appeared to be equally distributed between the cytosol and the particulate fraction; the level in both compartments increased during the major period of synapse formation. Thus, the development of calmodulin-dependent protein phosphatase closely parallels synaptogenesis, implicating a role in some synaptic function.     

Effects of alkali ions on myosin conformation

We have used two probes to study the effects of alkali ions on the conformation of myosin. One was paramagnetic, the “spin label” N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)-maleimide, which binds primarily to SH groups; and the other was fluorescent, l-anilino-8-naphthalenesulfonate, which binds to an apolar niche. The bonding of the spin label to myosin was carried out in 0.6M LiCl, 0.6M NaCl, or 0.6M KCl, and the resulting labeled myosin was studied in the same medium in which the myosin was labeled as well as in other alkali chlorides. The electron paramagnetic resonance spectra of the spin label showed that the structure of myosin in the vicinity of the labeled groups differed in the various salts. The protein surface in the region of the labeled groups restricted the rotational freedom of the spin label more in KCl than in any of the other salts. Although ions are known to influence the properties of myosin, our results show that these ions also effect the molecular structure. The fluorescence of l-anilino-8-naphthalenesulfonate, noncovalently attached to myosin in the presence of alkali chlorides, decreased progressively with increasing size of the cations, again showing the protein structure near the probe attachment to be a function of the cation, in the solvent. Ca²⁺ quenched the fluorescence of the bound probe, indicating an interaction between Ca²⁺ and the myosin molecule. The effect of Ca²⁺ on the fluorescence was greatest in KCl.