Comparison of ras-p21 bound to GDP and GTP: differences in protein and ligand dynamics

This paper documents the first essential dynamics analysis of ras protein ligands and of the protein itself, showing important features of their dynamic properties. Essential dynamics analysis of 300 ps of full solvent molecular dynamics simulations revealed differences in structure and dynamics between GDP- and GTP-bound forms of H-ras-p21. Regions in the protein which exhibited a structural shift correspond to the switch regions described previously. Differences in dynamics between H-ras-p21 GDP and H-ras-p21 GTP may be related to interactions of ras with GAP and its receptor and effector. Molecular dynamics of free GDP (in the absence of protein) were performed in water for 2 ns and analysed using essential dynamics. The conformations of GDP and GTP when bound to the protein were compared with free GDP, revealing that the ligands bind to the protein in an energetically unfavourable conformation. GDP and GTP molecules from various other protein crystal structures were also analysed. These ligands adopt similar conformations to those seen in H-ras-p21.      

Lack of effect of methenamine in suppression of, or prophylaxis against, chronic urinary infection

Methenamine is frequently prescribed for patients who have chronic urinary infection to suppress bacterial growth during active infection or to prevent recurrence once an infection has been brought under control. We have examined the effect of methenamine mandelate and ascorbic acid on bacteriuria in para- and quadriplegics from a spinal cord unit. Patients with indwelling urinary catheters and those on a program of intermittent catheterization were included. No suppressive or prophylactic effect of this regimen was observed in any of our patients. Methenamine does not appear to be an effective antimicrobial agent in subjects who have an indwelling urinary catheter or in patients with spinal cord injury who are on intermittent catheterization. Since there appears to be reason to question the efficacy of methenamine in situations in which it is usually prescribed, evidence should be sought for a therapeutic effect in other cases. If no benefit is observed, the drug should not be used.     

The ocular manifestations of Beh?et's disease

Of 32 patients with Beh?et's disease, 21 had uveitis. The uveitis was seldom the initial manifestation of systemic disease, but once established, it tended to become chronic and bilateral, involving the anterior and posterior segments. Hypopyon was a relatively uncommon occurrence in this series. All patients with uveal inflammation had obvious cellular reactions within the vitreous body. Other posterior segment manifestations of the disease included localized retinal edema, macular edema, disc edema, retinal pigmentary changes, and accumulation of exudative material in the deep retina. One patient developed a necrotizing retinitis with deep retinal exudation and subsequent retinal detachment. Occlusions of retinal vessels were common. Neuro-ophthalmologic manifestations of Beh?et's disease included cranial nerve palsies, a homonymous hemianopic field defect, and papillitis.     

Tuberculosis of the breast

Twenty-one cases of mammary tuberculosis are reported and the attendant clinical and histological difficulties described. It is probable that contemporary clinicians would now make the clinical diagnosis of breast abscess or carcinoma. Furthermore, the histological features (without demonstration or culture of the organism) may be confused with those granulomatous epithelloid reactions seen in mammary duct ectasia (comedo cell mastitis, plasma cell mastitis) and in traumatic fat necrosis.     

Effects of agitation on size distribution of particulate matter in large-volume parenterals

The particle-size distributions of six types of large-volume parenterals subjected to different degrees of agitation were determined using an automatic particle counter. Data acquired from each solution, which had been maintained in a stored condition, subjected to agitation by inverting 20 times, and then mechanically shaken for 30 min, produced a linear relationship between log N greater than D and log D. Both the slope (K) and the number of particles per milliliter exceeding 1 micrometer in diameter (N greater than 1) exhibited a dependence on the degree of agitation. Their combined effect indicates that agitation by 20 hand inversions removed particulate matter from the surface of the container, which increased the total number of particles in solution (greater than 1 micrometer) but did not significantly alter the relative size distribution. Agitation for 30 min, however, disintegrated agglomerates and produced a particle-size distribution with a greatly increased number of particles whose diameters were less than 1 micrometer and a corresponding decrease in the number of particles exceeding 1 micrometer in diameter. The particle-size distribution of a parenteral solution determined by this in situ instrumental method was, therefore, dependent upon the degree of agitation to which the parenteral was subjected prior to examination.     

Evidence for "twisted plane" undulations in golden hamster sperm tails

Motile spermatozoa from the golden hamster have been arrested by rapid freezing and then fixed with glutaraldehyde at low temperature after substitution with ethylene glycol. As far as can be judged, the flagellar waveforms thus stabilized are similar to those seen in living sperm; in contrast, fixation in glutaraldehyde, without prior freezing, induces agonal changes in flagellar conformation. The characteristics waveform after freeze substitution contains three bends. Approx. half of these flagella are entirely planar. The rest are three dimensional, with the third bend displaced in a regular way from the plane containing the proximal two bends. From the geometry of these flagella, it is concluded that the plane of action of a given bending cycle undergoes a clockwise twist (from a forward viewpoint) as the cycle is succeeded by new bending cycles. This "twisted plane" undulation is quite different from helical movement. The twisting seems to occur abruptly, between cycles, as if each bending cycle has a preferred plane of action. The mechanism underlying the twisting is uncertain. However, on the basis of the angular displacements between the preferred planes, and the findings from electron microscopy, the following idea is presented as a working hypothesis: that, if the most proximal plane of bending is topographically determined by peripheral doublet 1, then successive distal planes of action are influenced predominantly by doublets 2, 3, etc., in clockwise sequence. The merits and weaknesses of this hypothesis are discussed.     

Medial calcinosis of M?nckeberg. A review of the problem and a description of a patient with involvement of peripheral, visceral and coronary arteries

Massive medial calcific deposits (M?nckeberg's calcinosis) are described in the peripheral and visceral arteries, and similar but small-sized deposits in the coronary arteries of a 41 year old woman with diabetes mellitus. Although observed by roentgenogram fairly commonly during life in the muscular arteries of the legs in middle-aged men, medial calcinosis infrequently involves the visceral arteries and has never, to our knowledge, been documented in the coronary arteries. Although it may be associated with intimal atherosclerosis, medial calcinosis, per se, does not obstruct the lumens of the arteries and, therefore, does not lead to symptoms or signs of limb or organ ischemia. The cause of medial calcinosis remains a mystery, but it appears to affect people with diabetes more frequently than those without.     

Amino acid concentrations in portal venous plasma during absorption from the small intestine of the guinea pig of an amino acid mixture simulating casein and a partial enzymic hydrolysate of casein

1. The characteristics of absorption of individual amino acids from amino acid mixtures simulating casein and from enzymic hydrolysates of casein containing oligopeptides as well as free amino acids are known to be different. The differences, which are attributable to mucosal uptake of small peptides, involve more rapid absorption from the enzymic hydrolysates of certain amino acids which are relatively slowly absorbed from the amino acid mixtures. This could lead to more effective utilization of amino acids from the enzymic hydrolysates than from the amino acid mixtures. 2. To obtain further information bearing on this hypothesis, we have used a recently developed technique for portal cannulation in the guinea pig to make a preliminary investigation of amino acid concentrations in the portal venous plasma at intervals after the infusion into the duodenum of equivalent amounts of (a) an amino acid mixture simulating casein and (b) a partial enzymic (papain followed by kidney peptidases) hydrolysate of casein, the two preparations being infused in separate experiments. 3. For some amino acids, such as leucine, isoleucine, valine, phenylalanine and lysine, the curves after the enzymic hydrolysate were fairly similar to the corresponding curves after the amino acid mixture, though usually slightly lower. With other amino acids, the curves after the enzymic hydrolysate were very much lower than the corresponding curves after the amino acid mixture. With serine, glutamine, proline and glycine this discrepancy was particularly great. 4. The results cannot yet be fully explained, but their main features are explicable by the hypothesis that the lower amino acid concentrations in portal plasma after the enzymic hydrolysate are the result of entry of amino acids into the portal blood in peptide form, in which they would not be detectable by the analytical technique employed, and possibly also of more rapid clearance of amino acids from the blood during absorption of this preparation.