Venous pressure and exercise tolerance.

Compared to the number of contractions obtained when a blood pressure cuff on the upper arm was at zero pressure, inflation of the cuff to pressures ranging between 5 and 40 mm Hg resulted in an augmentation of the number of hand contractions that could be performed prior to the development of ipsilateral severe fatigue or intolerable pain. Cuff pressures of 60 mm Hg reduced the number of contractions below the control level. These results are consistent with the concept that exercise during venous congestion facilitates the washout of the toxic catabolite presumed to be produced during muscular contraction.     

Pyrithioxine: a new basic treatment of rheumatoid arthritis. Open study of 60 cases with a follow-up of 6 months

Pyrithioxine, a chemical compound with several points in common with penicillinamine, was used for six months as the basic treatment in a series of 60 cases of rheumatoid arthritis, in a dose of 600 mg per day. The results were favourable in 60 per cent of cases, with a marked fall in articular index, a return to normal of sedimentation rate and, less commonly, negativisation of the Rose-Waaler reaction. Side effects were essentially cutaneo-mucosal (pruitus, rash) and necessitated the interruption of treatment in 16.5 per cent of cases. No complications were seen. Compared with penicillinamine, pyrithioxine appears to be less effective but better tolerated. The place of this new basic drug in the basic treatment of rheumatoid arthritis remains to be precisely determined.     

Improvement of regional myocardial metabolism after coronary thrombolysis induced with tissue-type plasminogen activator or streptokinase

To assess the effects on the heart itself of coronary thrombolysis induced with either tissue-type plasminogen activator (t-PA) or streptokinase (SK), we performed positron emission tomography with 11C-palmitate in 19 patients with initial transmural myocardial infarction immediately after admission and again within 48 to 72 hr after intracoronary administration of t-PA (n = 2) or SK (n = 17). Clots were persistent in eight patients treated with SK despite an average dose of 336,000 IU, sufficient to markedly deplete fibrinogen. In the absence of lysis, favorable tomographic changes did not occur. In contrast, in each of the 11 patients in whom lysis was induced (two with t-PA and nine with SK) myocardial accumulation of 11C-palmitate improved by an average of 29% in late compared with early studies (p less than .001). Results were comparable in patients with anterior and those with inferior infarction. Thus clot lysis induced with either t-PA or SK led to improved regional myocardial metabolism.     

Ghrelin secretion in humans is sexually dimorphic,suppressed by somatostatin,and not affected by the ambient growth hormone levels

We studied plasma ghrelin and GH concentrations over a 24-h period in young healthy men and women and in patients with acromegaly. Healthy subjects were restudied after administration of GH-lowering agents, octreotide or GHRH antagonist. Ghrelin concentrations in women studied during the late follicular stage of the cycle were about 3-fold higher than in men. Suppression of GH secretion by GHRH antagonist did not alter ghrelin concentration profiles. In the presence of high GH levels (acromegaly), ghrelin levels were similar to those found in healthy men. Administration of somatostatin analog octreotide suppressed both GH and ghrelin concentration profiles. We conclude that: 1) ghrelin secretion is sexually dimorphic in humans, with women in the late follicular stage having higher levels than men; 2) ghrelin secretion is suppressed by somatostatin; and 3) GH has no influence over ghrelin secretion.     

Trends and seasonality of antibiotic resistance of Neisseria gonorrhoeae.

Over 8,400 pretreatment isolates of Neisseria gonorrhoeae collected in the United States between November 1972 and April 1975 were tested for their in vitro resistance to penicillin, ampicillin, tetracycline, and spectinomycin. Trends and seasonality of resistance were examined by use of a harmonic regression technique. During the study period, there was a significant difference among years in the mean minimal inhibitory concentrations (MICs) for each antibiotic (P less than 0.001 for penicillin, ampicillin, and tetracycline; P less 0.05 for spectinomycin), and the mean MIC for each antibiotic decreased. Resistance to tetracycline and penicillin was highest in the winter months. Seasonality of resistance, alone or as an interaction with year, approached significance (P less than 0.10) or was significant (P less than 0.05) for all four antibiotics.     

First structure of full-length mammalian phenylalanine hydroxylase reveals the architecture of an autoinhibited tetramer

Improved understanding of the relationship among structure, dynamics, and function for the enzyme phenylalanine hydroxylase (PAH) can lead to needed new therapies for phenylketonuria, the most common inborn error of amino acid metabolism. PAH is a multidomain homo-multimeric protein whose conformation and multimerization properties respond to allosteric activation by the substrate phenylalanine (Phe); the allosteric regulation is necessary to maintain Phe below neurotoxic levels. A recently introduced model for allosteric regulation of PAH involves major domain motions and architecturally distinct PAH tetramers [Jaffe EK, Stith L, Lawrence SH, Andrake M, Dunbrack RL, Jr (2013) Arch Biochem Biophys 530(2):73–82]. Herein, we present, to our knowledge, the first X-ray crystal structure for a full-length mammalian (rat) PAH in an autoinhibited conformation. Chromatographic isolation of a monodisperse tetrameric PAH, in the absence of Phe, facilitated determination of the 2.9 Å crystal structure. The structure of full-length PAH supersedes a composite homology model that had been used extensively to rationalize phenylketonuria genotype–phenotype relationships. Small-angle X-ray scattering (SAXS) confirms that this tetramer, which dominates in the absence of Phe, is different from a Phe-stabilized allosterically activated PAH tetramer. The lack of structural detail for activated PAH remains a barrier to complete understanding of phenylketonuria genotype–phenotype relationships. Nevertheless, the use of SAXS and X-ray crystallography together to inspect PAH structure provides, to our knowledge, the first complete view of the enzyme in a tetrameric form that was not possible with prior partial crystal structures, and facilitates interpretation of a wealth of biochemical and structural data that was hitherto impossible to evaluate.Mammalian phenylalanine hydroxylase (PAH) (EC 1.14.16.1) is a multidomain homo-multimeric protein whose dysfunction causes the most common inborn error in amino acid metabolism, phenylketonuria (PKU), and milder forms of hyperphenylalaninemia (OMIM 261600) (1). PAH catalyzes the hydroxylation of phenylalanine (Phe) to tyrosine, using nonheme iron and the cosubstrates tetrahydrobiopterin and molecular oxygen (2, 3). A detailed kinetic mechanism has recently been derived from elegant single-turnover studies (4). PAH activity must be carefully regulated, because although Phe is an essential amino acid, high Phe levels are neurotoxic. Thus, Phe allosterically activates PAH by binding to a regulatory domain. Phosphorylation at Ser16 potentiates the effects of Phe, with phosphorylated PAH achieving full activation at lower Phe concentrations than the unphosphorylated protein (5, 6). Allosteric activation by Phe is accompanied by a major conformational change, as evidenced by changes in protein fluorescence and proteolytic susceptibility, and by stabilization of a tetrameric conformer (3).There are >500 disease-associated missense variants of human PAH; the amino acid substitutions are distributed throughout the 452-residue protein and among all its domains (Fig. 1A) (7–9). Of those disease-associated variants that have been studied in vitro (e.g., ref. 10), some confound the allosteric response, and some are interpreted as structurally unstable. We also suggest that the activities of some disease-associated variants may be dysregulated by an altered equilibrium among conformers having different intrinsic levels of activity, arguing by analogy to the enzyme porphobilinogen synthase (PBGS) and its porphyria-associated variants (11). Consistent with this notion, we have recently established that PAH can assemble into architecturally distinct tetrameric conformers (12), and propose that these conformers differ in activity due to differences in active-site access. This idea has important implications for drug discovery, as it implies that small molecules could potentially modulate the conformational equilibrium of PAH, as has already been demonstrated for PBGS (e.g., ref. 13). Deciphering the relationship among PAH structure, dynamics, and function is a necessary first step in testing this hypothesis.Open in a separate windowFig. 1.The structure of PAH. (A) The annotated domain structure of mammalian PAH. (B) The 2.9 Å PAH crystal structure in orthogonal views, colored as in part A, subunit A is shown in ribbons; subunit B is as a Cα trace; subunit C is in sticks; and subunit D is in transparent spheres. In cyan, the subunits are labeled near the catalytic domain (Top); in red, they are labeled near the regulatory domain (Bottom). The dotted black circle illustrates the autoregulatory domain partially occluding the enzyme active site (iron, in orange sphere). (C) Comparison of the subunit structures of full-length PAH and those of the composite homology model; the subunit overlay aligns residues 144–410. The four subunits of the full-length PAH structure (the diagonal pairs of subunits are illustrated using either black or white) are aligned with the two subunits of 2PAH (cyan) and the one subunit of 1PHZ (orange). The catalytic domain is in spheres, the regulatory domain is in ribbons, and the multimerization domain is as a Cα trace. The arrow denotes where the ACT domain and one helix of 2PAH conflict.Numerous crystal structures are known for one- and two-domain constructs of mammalian PAH (14).

Table S1.

Mammalian PAH structures available in the PDB (August 2015)