Receptor activation of G proteins

G proteins are a highly conserved family of membrane-associated proteins composed of alpha, beta, and gamma subunits. The alpha subunit, which is unique for each G protein, binds GDP or GTP. Receptors such as those for beta- and alpha-adrenergic catecholamines, muscarinic agonists, and the retinal photoreceptor rhodopsin, catalyze the exchange of GDP for GTP binding to the alpha subunit of a specific G protein. G alpha.GTP regulates appropriate effector enzymes such as adenylyl cyclase or the cyclic GMP phosphodiesterase. The beta gamma-subunit complex of G proteins is required for efficient receptor-catalyzed alpha subunit guanine nucleotide exchange and also functions as an attenuator of alpha subunit activation of effector enzymes. Recent elucidation of both receptor and G protein primary sequence has allowed structural predictions and new experimental approaches to study the mechanism of receptor-catalyzed G protein regulation of specific effector systems and the control of cell function including metabolism, secretion, and growth.     

Correlation between manganese-deficiency,loss of respiratory chain complex I activity and citric acid production in Aspergillus niger

The correlation between manganese deficiency, loss of mitochondrial respiratory chain NADH: ubiquinone oxidoreductase (complex I) activity and citric acid overproduction in the Aspergillus niger strain B 60 was analysed. With increasing manganese-supplementation of the production medium the loss of complex I activity and the production of citric acid was reduced. Addition of manganese during growth stopped further loss of complex I activity and further increase of citric acid production. A possible causality between complex I deficiency and citric acid overproduction is discussed.     

The relationship between short-term memory capacity and EEG power spectral density

Multiplying memory span by mental speed, we obtain the information entropy of short-term memory capacity, which is rate-limiting for cognitive functions and corresponds with EEG power spectral density. The number of EEG harmonics (n = 1, 2,, 9) is identical with memory span, and the eigenvalues of the EEG impulse response are represented by the zero-crossings up to the convolved fundamental, the P300. In analogy to quantum mechanics the brain seems to be an ideal detector simply measuring the energy of wave forms. No matter what the stimulus is and how the brain behaves, the metric of signal and memory can always be understood as a superposition of n states of different energy and their eigenvalues.     

Management of the recalcitrant total-hip arthroplasty wound

The infection rate for total-hip arthroplasty is around 1 percent. This small group is usually managed by complete removal of the prosthesis and the cement and closure over suction catheters to "collapse" the wound and eventually achieve a girdlestone arthroplasty. Occasionally, there are patients who have a persistent draining wound after this treatment and repeated efforts at wound closure. We present 27 patients who had recalcitrant, noncollapsible wounds of the hip that were present for many months to years. Twenty-eight cases of infected total-hip arthroplasties that did not respond to removal of the prosthesis and cement and closure were seen by the authors between January of 1977 and December of 1988. One patient had bilateral involvement. Average age was 64 years (range 33 to 79 years). There was an average of 4.2 previous surgical attempts at closure (range 1 to 21). Staphylococcus aureus was the most common organism, but the infections were virtually all multiple. Thirty-three muscles were utilized in 27 patients. The rectus femoris was used in 23 cases, the vastus lateralis in 8, tensor fasciae latae in 1, and combined latissimus dorsi-serratus anterior free-tissue transfers were carried out in 2. Multiple combinations of transpositions and free flaps were utilized. Follow-up ranged from 1 to 10 years, with an average of 6.4 years. Eighteen patients were ambulatory with minor degrees of pain, five ambulated with a cane, seven ambulated with a walker, six ambulated with crutches, and four ambulated unassisted, all of whom had reimplantation of their hip arthroplasty at least 12 months following the muscle flap procedure.(ABSTRACT TRUNCATED AT 250 WORDS)     

A light-dependent dicyclohexylcarbodiimide-sensitive Ca-ATPase activity in chloroplasts which is not coupled to proton translocation

The early observation of light-dependent Ca-ATPase activity in chloroplast thylakoids [Avron, M. (1962) J. Biol. Chem. 237, 2011-2017] has been reinvestigated. It is demonstrated that in contrast to light-triggered Mg-ATP activity, Ca-ATPase activity is strictly dependent on delta microH+, the transthylakoid membrane electrochemical potential gradient, since (a) there is an absolute requirement for continuous illumination; (b) electron-transport mediators that catalyze proton uptake, like phenazinemethosulphate, methylviologen of ferricyanide, are essential and (c) uncouplers inhibit the activity. The Ca-ATPase activity is essentially unaffected by dithiols, but is inhibited by CF0-CF1 inhibitors including tentoxin, dicyclohexylcarbodiimide and antisera to CF1. Addition of Ca-ATP to thylakoids does not induce delta pH or delta psi (the electrical potential gradient) formation either in the light or following preillumination with dithiols, demonstrating that it is not coupled to proton translocation. It is also demonstrated that Ca-ATP or Ca-ADP does not induce a proton leak through CF0-CF1. It is concluded that the Ca-ATPase activity in chloroplast thylakoid reflects a partial reaction of ATP synthesis catalyzed by CF0-CF1, which is internally uncoupled from proton translocation but is dependent on energization by a transmembrane delta microH+.     

Glutamate biosynthesis in Bacillus azotofixans. 15N NMR and enzymatic studies

Pathways of ammonia assimilation into glutamic acid in Bacillus azotofixans, a recently characterized nitrogen-fixing species of Bacillus, were investigated through observation by NMR spectroscopy of in vivo incorporation of 15N into glutamine and glutamic acid in the absence and presence of inhibitors of ammonia-assimilating enzymes, in combination with measurements of the specific activities of glutamate dehydrogenase, glutamine synthetase, glutamate synthase, and alanine dehydrogenase. In ammonia-grown cells, both the glutamine synthetase/glutamate synthase and the glutamate dehydrogenase pathways contribute to the assimilation of ammonia into glutamic acid. In nitrate-grown and nitrogen-fixing cells, the glutamine synthetase/glutamate synthase pathway was found to be predominant. NADPH-dependent glutamate dehydrogenase activity was detectable at low levels only in ammonia-grown and glutamate-grown cells. Thus, B. azotofixans differs from Bacillus polymyxa and Bacillus macerans, but resembles other N2-fixing prokaryotes studied previously, as to the pathway of ammonia assimilation during ammonia limitation. Implications of the results for an emerging pattern of ammonia assimilation by alternative pathways among nitrogen-fixing prokaryotes are discussed, as well as the utility of 15N NMR for measuring in vivo glutamate synthase activity in the cell.     

Characterization of SV40 chromatin by mass determination on STEM

Direct mass determination of purified SV40 minichromosomes was obtained by scanning transmission electron microscopy. Twenty to thirty percent of the minichromosomes were found with an Mr of 6.9±0.4×10⁶. The rest of the molecules formed a spread Mr distribution ranging from 7.3×10⁶ to 9.5×10⁶ due possibly to different contents of the virus-coded proteins, mainly VP1. The apparent mass histogram of individual SV40 nucleosomes presents three maxima at Mr 2.1×10⁵, 2.6×10⁵ and 3.1×10⁵ that could correspond to partially unravelled nucleosomes, complete nucleosomes and complete nucleosomes with the addition of VP1. Beaded structures with a higher mass were also measured; some were found at either side of the open nucleosome-free region.     

A transferrin receptor antibody represents one signal for the induction of IL 2 production by a human T cell line

We previously demonstrated a two-signal requirement for the activation of the human T cell lines Jurkat and HUT 78. Interleukin 2 (IL 2) production by these lines can be induced by phytohemagglutinin (PHA), T3 antibodies, or calcium ionophores, but only in combination with phorbol myristate acetate (PMA). To obtain further information about surface structures involved in T cell activation, we produced a monoclonal antibody that could substitute for PMA in the activation of HUT 78. This antibody, designated J64, induced IL 2 secretion by HUT 78 in combination with PHA, T3 antibodies, or calcium ionophores, however not by itself. J64 also had other PMA-like effects on HUT 78, such as an increase in IL 2 receptor expression and an inhibition of cell growth. J64 was shown to immunoprecipitate the transferrin receptor (TfR). However, it bound to an epitope different from those recognized by other TfR antibodies and different from the transferrin-binding site. In addition, other previously described TfR antibodies did not, like J64, function as activating stimuli for HUT 78. Possible mechanisms for activation signaling in T cells involving the TfR are discussed.