Maleylacetone cis-trans-isomerase: affinity chromatography on glutathione-bound sepharose. Two-substrate-binding sequence from inhibition patterns

Maleylacetone cis-trans-isomerase isolated from Vibrio 01 binds glutathione strongly; Km = 1.4 X 10(-4) M. Oxidized glutathione and S-methylglutathione are competitive inhibitors, KI = 9.4 X 10(-4) and 1.2 X 10(-3) M, respectively. Based on these interactions, three different glutathione-bound agarose affinity adsorbents were synthesized and tested. Affinity chromatography of the isomerase with one of these affords 70- to 100-fold purifications. In separate syntheses, portions of the affinity arm were prepared and examined as to their inhibitory properties in the enzyme-catalyzed reaction. The fragment, containing glutathione bound through its sulfur to the carbon chain, is a powerful competitive inhibitor for glutathione (KI = 6 X 10(-5) M). The results described suggest that the isomerase binds glutathione through the backbone of the tripeptide and that the thiol group is required for activity. The initial velocity patterns of the enzyme-catalyzed reaction resulting from simultaneous variation of glutathione and maleylacetone concentrations were examined in the absence and presence of inhibitors resembling glutathione. The observed kinetic patterns suggest an ordered sequence of binding maleylacetone first followed by glutathione.     

Effects of increased O2-N2 pressure and breathing apparatus on respiratory function

The ventilatory response of four subjects was measured at rest and various intensities of exercise. Experiments were conducted in a dry pressure chamber (1) at 1 ATA and 4 ATA with the subjects breathing from a low-resistance mouthpiece, and (2) at ATA with the subjects breathing from open-circuit breathing apparatus (Royal Naval Swimmers' Air Breathing Apparatus). At 4 ATA there was significant hypoventilation and hypercapnia, together with an increased tidal volume and lower respiratory frequency. The use of the breathing apparatus tended to amplify these changes in ventilatory response. In addition, the extent of hypercapnia at 4 ATA was related to the exercise intensity. When subjects breathed from a low-resistance mouthpiece, oxygen uptake was significantly greater at 4 ATA than at the surface for the same ergometric work load, but when they breathed from the breathing apparatus, the increase in oxygen uptake was not significant in comparison to surface values. At 4 ATA bradycardia was evident at all levels of exercise but was not affected significantly by the presence of the breathing apparatus.     

A behavioural programme for the modification of encopresis

This paper describes a behaviour modification programme for the treatment of encopresis. The programme, which is carried out by the parents over a relatively short period of time in the home setting, aims to make the child aware of internal cues prior to elimination and to rearrange the contingencies for appropriate use of the toilet. To date, seven of eleven children, both continuous and discontinuous encopretics, have been treated successfully and have remained clean for up to 7 months regardless of other problems in the child and his family. From a relatively detailed analysis of those treated it can be concluded that a behavioural approach is effective with chronic encopretic children, many of whom had been previously treated unsuccessfully by both physical and psychotherapeutic procedures. The failures suggest, firstly that careful assessment of each child and the motivation of the parents is required, so that the standard programme can be modified to suit each individual case. Secondly a maintenance programme must follow the intensive treatment procedure to ensure that parents continue to handle the child consistently.     

A practical evaluation system for preclinical restorative dentistry

This paper describes an attempt to build a functional evaluation system incorporating several aspects of the evaluation process that have been advocated in educational research. The system--which employs performance criteria, analytical grading, rater calibration, student self-evaluation, mark-sense grading forms, and computer tabulation--has been in effect for six years at the Medical College of Georgia School of Dentistry. The main advantages of this approach are prompt, specific feedback to students concerning their performance on practical exams and diagnostic aids to course directors. In addition, rater calibration has resulted in interrater reliability usually around 0.80 or higher. The major disadvantages of the system are the faculty time required and dependence on a computer.     

Application of solid-phase microextraction and gas chromatography-mass spectrometry for the determination of chlorophenols in urine

Previously, we have demonstrated that chronic exposure to immobilization (IMO) did not modify the influence of catecholamines on active behaviour of rats in the holeboard, but clearly increased the role of these amines in the forced swimming test (FST). In the present experiment, it was studied whether or not chronic IMO altered the role of dopamine in the two tests. Adult male Sprague-Dawley rats were left either undisturbed or subjected daily to 2 h of IMO stress for 12 days. On the following day, half of the rats were administered saline and the others the dopamine antagonist haloperidol (0.5 mg/kg). Then the rats remained undisturbed in the animal room (controls) or were subjected to acute IMO for 2 h. Finally, all animals were exposed consecutively to the holeboard (4 min) and the FST (5 min). In non-chronically stressed rats, acute IMO depressed behaviour in the holeboard but not in the FST. In chronic IMO rats the inhibitory effect of acute IMO on holeboard activity was slightly reduced as compared to controls. Acute IMO increased struggling in rats previously exposed to chronic IMO but did not alter struggling in non-chronically stressed rats. Whereas the inhibition caused by haloperidol treatment in the active behaviour of rats in the holeboard was not altered by chronic IMO, the inhibitory effect of haloperidol in the active behaviour of rats in the FST was greater after chronic IMO, particularly in rats also subjected to acute IMO. These data suggest that chronic IMO stress potentiates the role of dopamine in a specific behavioural task such as the FST and adds support to the previously published data demonstrating enhanced behavioural and neurochemical responses to dopamine-related drugs after chronic stress.     

Experimental liver injury: serial splenoportography and post-mortem angiography by means of Schlesinger''s mass

Out of 222 eyes with diabetic retinopathy, observed during a period of 6-42 months after argon laser photocoagulation, 66 (30%) became worse. The most common complication was a fast increase of previous existing macular oedema due to extensive and heavy macular treatment. Another complication was an increase of the neovascularisation due to the inadequate treatment of avascular zones and heavy-leaking areas and to the growth of the neovascular tuft after the feeder vessel technique without previous peripheral ablation. Retinal and vitreal haemorrhages were frequent in this group. Fibrous tissue formation and vascular pseudopapillitis were less frequent complications. Large coagulations outside the macular area (peripheral ablation) are necessary to destroy the zones of borderline nutritional supply, which probably are closely related to the new vessel formation. The feeder vessel technique must not be used without a peripheral ablation although it may be of great help in destroying prepapillary or large neovascularisation.     

Response of HeLa cells to irradiation with pi- mesons

HeLa cell suspensions were irradiated at various depths of Perspex in a beam of 70 MeV pi- mesons. The dose-rate in the Bragg peak varied between 40 rad hour-1 and 150 rad hour-1. The cells were assayed in vitro for loss of reproductive integrity. The results for irradiation in the peak indicated an RBE of about 2-1 when compared to the response obtained using 60Co gamma-rays at comparable dose-rates. At dose-rates of 100-150 rad hour-1, the RBE peak-to-plateau was about 1-4, while at lower dose-rates, the RBE peak-to-plateau was about 1.