A new remote subsite in ribonuclease A

The interaction between bovine pancreatic ribonuclease A (RNase A) and its RNA substrate extends beyond the scissile bond. Enzymic subsites interact with the bases and the phosphoryl groups of a bound substrate. We evaluated the four cationic residues closest to known subsites for their abilities to interact with a bound nucleic acid. Lys-37, Arg-39, Arg-85, and Lys-104 were replaced individually by an alanine residue, and the resulting enzymes were assayed as catalysts of poly(cytidylic acid) (poly(C)) cleavage. The values of Km and kcat/Km for poly(C) cleavage were affected only by replacing Arg-85. Moreover, the contribution of Arg-85 to the binding of the ground state and the transition state was uniform---Km increased by 15-fold and kcat/Km decreased by 10-fold. The contribution of Arg-85 to binding was also apparent in the values of Kd for complexes with oligonucleotides of different length. This contribution was dependent on salt concentration, as expected from a coulombic interaction between a cationic side chain and an anionic phosphoryl group. Together, these data indicate that Arg-85 interacts with a particular phosphoryl group of a bound nucleic acid. We propose that Arg-85 comprises a new distal subsite in RNase A---the P(-1) subsite.     

Autoinducer of virulence as a target for vaccine and therapy against Staphylococcus aureus

Staphylococcus aureus causes pathologies ranging from minor skin infections to life-threatening diseases. Pathogenic effects are largely due to production of bacterial toxin, which is regulated by an RNA molecule, RNAIII. The S. aureus protein called RAP (RNAIII activating protein) activates RNAIII, and a peptide called RIP (RNAIII inhibiting peptide), produced by a nonpathogenic bacteria, inhibits RNAIII. Mice vaccinated with RAP or treated with purified or synthetic RIP were protected from S. aureus pathology. Thus, these two molecules may provide useful approaches for the prevention and treatment of diseases caused by S. aureus.     

Phosphorylation of the periplasmic binding protein in two transport systems for arginine incorporation in Escherichia coli K-12 is unrelated to the function of the transport system

In Escherichia coli K-12, the accumulation of arginine is mediated by two distinct periplasmic binding protein-dependent transport systems, one common to arginine and ornithine (AO system) and one for lysine, arginine, and ornithine (LAO system). Each of these systems includes a specific periplasmic binding protein, the AO-binding protein for the AO system and the LAO-binding protein for the LAO system. The two systems include a common inner membrane transport protein which is able to hydrolyze ATP and also phosphorylate the two periplasmic binding proteins. Previously, a mutant resistant to the toxic effects of canavanine, with low levels of transport activities and reduced levels of phosphorylation of the two periplasmic binding proteins, was isolated and characterized (R. T. F. Celis, J. Biol. Chem. 265:1787-1793, 1990). The gene encoding the transport ATPase enzyme (argK) has been cloned and sequenced. The gene possesses an open reading frame with the capacity to encode 268 amino acids (mass of 29.370 Da). The amino acid sequence of the protein includes two short sequence motifs which constitute a well-defined nucleotide-binding fold (Walker sequences A and B) present in the ATP-binding subunits of many transporters. We report here the isolation of canavanine-sensitive derivatives of the previously characterized mutant. We describe the properties of these suppressor mutations in which the transport of arginine, ornithine, and lysine has been restored. In these mutants, the phosphorylation of the AO- and LAO-binding proteins remains at a low level. This information indicates that whereas hydrolysis of ATP by the transport ATPase is an obligatory requirement for the accumulation of these amino acids in E. coli K-12, the phosphorylation of the periplasmic binding protein is not related to the function of the transport system.     

Percutaneous transluminal angioplasty for the treatment of limb threatening ischemia: do the results justify an attempt before bypass grafting?

PURPOSE: Results of percutaneous transluminal angioplasty (PTA) in selected cases have been reported to be equal or superior to those of arterial bypass graft surgery, with a lower morbidity and mortality. We performed PTA of stenotic or occlusive lesions in patients with limb-threatening ischemia, hoping to improve our overall success and decrease morbidity in this group of patients. The results of PTA in the limb-salvage setting was evaluated. METHODS: From 1992 to 1995, 307 PTAs were performed in 257 patients. One hundred sixty-one (63%) patients had diabetes mellitus, and 32 (12%) patients had renal failure. All patients were evaluated by means of pulse volume recordings and ankle brachial indices at 1 and 6 weeks after PTA and at 3 month intervals thereafter. Seventeen patients (9%) were lost to follow-up. The continued success or failure of PTA was defined by means of noninvasive vascular laboratory criteria, patency by means of pulse examination, the need for subsequent bypass grafting across the index lesion, and limb salvage. RESULTS: The 1-year patency rates for external iliac PTAs (56%) were significantly lower (P <.05) than those for common iliac PTAs (87%). Infrainguinal PTAs at the femoral, popliteal, and tibial level had 1-year patency rates of less than 15%. CONCLUSION: Common iliac artery PTA is justified in most cases in which it is feasible. However, when PTAs are performed below the inguinal ligament, the results are markedly worse. One-year patency rates of PTA in this group of patients with threatened limbs are inferior to the patency rates of arterial bypass grafts, even when these bypasses are performed with a prosthetic material. PTA should not be considered as a primary treatment modality for patients with infrainguinal arterial occlusive disease who also have limb-threatening ischemia, except in unusual circumstances.     

A special fluorescent in situ hybridization technique to study peripheral blood and assess the effectiveness of interferon therapy in chronic myeloid leukemia

Using a highly sensitive fluorescence in situ hybridization method with probes for BCR and ABL1 (D-FISH), we studied 37 paired sets of bone marrow and blood specimens, collected within 24 to 96 hours of each other, from 10 patients before and during treatment for chronic myeloid leukemia (CML). The normal range for 500 interphase nuclei was 相似文献   

Does growth hormone prevent or accelerate aging?

It is very well documented that plasma growth hormone (GH) levels decline with age in the human and in experimental animals, and there is considerable evidence that age-related changes in body composition may be caused by reduced function of the GH-IGF-I system. However, excessive GH levels are associated with reduced life expectancy in acromegalic patients and with symptoms of accelerated aging in GH transgenic mice. Hereditary dwarf mice deficient in GH, prolactin, and TSH live much longer than their normal siblings. Possible mechanisms of delayed aging in dwarf mice include lower core body temperature and reduced oxidative processes. It is suggested that the controversies concerning the apparent potential of GH to both prevent and accelerate aging may be reconciled by interpreting the results in light of the negative relationship between body size and life span within a species.