Thionesters as a probe for electrophilic catalysis in the serine protease mechanism

Specific and nonspecific thionester substrates for alpha-chymotrypsin and subtilisin Carlsberg have been synthesized and the kinetic parameters for their enzyme-catalyzed hydrolyses measured. Despite equal nonenzymic reactivities of ester-thionester pairs, each thionester is considerably less reactive toward enzymic hydrolysis, the difference being greatest for the specific substrates. The data support the operation of electrophilic catalysis by a hydrogen bond network at the carbonyl oxygen adjacent to the scissile bond of the substrate. The free energy of stabilization is 19 kJ mol-1 for a specific thionester substrate and will be higher for oxygen esters and amides. Chymotrypsin binds esters and thionesters about equally well, whereas subtilisin binds thionesters more tightly. This is consistent with continuous hydrogen bonding in the chymotrypsin mechanism and with a differential hydrogen bonding mechanism for subtilisin. A comparison of the relative rates of enzyme-catalyzed hydrolysis of ester and thionester substrates with their relative reactivities toward amines does not support an acyl histidine intermediate in the serine protease mechanism.

13C-nuclear magnetic resonance studies of sugar cataractogenesis in the single intact rabbit lens

In this report we demonstrate that 13C-nuclear magnetic resonance spectroscopy may be used to monitor the sorbitol and glycolytic pathways in a single, intact, crystalline lens of the rabbit, thereby providing a new, noninvasive method for the study of sugar cataractogenesis. This approach is particularly useful for the measurement of intralenticular metabolic fluxes in single lenses under various conditions, at a time resolution previously unavailable in lens biochemistry.

Arterial vasa vasorum: a quantitative study in the rat

This study was designed to quantitate the vasa vasorum of common iliac arteries in 20 rats. The number of vasa vasorum per mm2 of arterial wall was extremely variable - from 0 to 124, the mean being 33 . 95 +/- 29 . 86 (S.D.). There was no significant difference in the vasa vasorum vascularity between the right and left common iliac arteries. The mean wall thickness of these arteries was 0 . 085 +/- 0 . 015 (S.D.) mm and 60 +/- 8% (S.D.) of this was made up by the tunica media. Arterial tissue in this study was shown to have approximately 10% of the vascularity of muscle tissue. By relating these data to the 'critical depth' hypothesis, on the nutritional supply of large arteries, it was concluded that the vasa vasorum in the common iliac arteries in rat (major arteries in small animals) probably play an insignificant role in the nutrition of the arterial wall.

Tetraploidy in a liveborn infant with spina bifida and other anomalies

Although tetraploidy of human chromosomes (92,XXYY) has been described frequently in abortuses, only one example in a liveborn infant has previously been described. A second malformed infant with a complete tetraploid chromosome complement, who lived for 15 days, is reported. In addition to many of the malformations described in the first case, this infant also had a sacral myelomeningocele and skeletal anomalies. The probable origin of the tetraploidy was a failure of cytoplasmic cleavage at the first mitotic division of the fertilised ovum.

Vein to artery grafts. A quantitative study of revascularization by vasa vasorum and its relationship to intimal hyperplasia

Iliolumbar vein to iliac artery grafts were placed in 40 rats by microsurgical technique. Groups of animals were perfused with fixative at eight intervals between one and 20 weeks after operation, and sections of the graft and control arteries (the opposite iliacs) were analyzed microscopically. The revascularization of the graft by capillaries commenced within the first postoperative week. The level of vascularity (capillaries per cross-sectional mm2) increased during the first four weeks, maintained a constant level and declined after week 16. The grafts of the 17--20 week group were substantially less vascular than the earlier groups. Intimal thickening commenced at three to four weeks after operation, i.e. during the period of increasing graft vascularity. The mean intimal proportion of the graft was 14% at four to five weeks and at 17--20 weeks was 35% of the cross-sectional area of the graft wall. However, the actual thickness of the intima did not increase significantly with time, rather the whole graft wall tended to become thinner. At 17--20 weeks grafts which showed a high degree of intimal thickening had significantly fewer capillaries within their walls. Quantitative evidence is presented to suggest that the continued growth of the graft intima may not be supported by a similar increase in the number of vasa vasorum. Therefore, it is suggested that the reduced level of vascularity in grafts with hyperplastic intimae may form an ischemic basis for degenerative changes which are known to take place in some long-term grafts.

A novel method for purification of prephenic acid

Prephenic acid accumulated in culture filtrates of Neuro-spora crassa has been purified in 66% yield utilizing adsorption chromatography on Sephadex G-10 in the major purification steps.

Asphyxiating thoracic dysplasia. Clinical, radiological, and pathological information on 10 patients

Review of 10 cases of asphyxiating thoracic dysplasia has shown a wide range of clinical effects and some variability in the radiographic features. Respiratory difficulty was severe in 7 babies and lethal in 6 of these. The seventh child is remarkable for his normal stature and excellent health at 15 years of age. 3 babies had no respiratory difficulty but 2 of them subsequently died of renal failure; one remains alive at 3 years. Microscopical abnormalities in the liver and kidneys were very frequent and appeared to increase progressively with age.

Natural Water and Chemical Budgets for a Small Precambrian Lake Basin in Central Canada

Results of a 4-yr study of the hydrology of the Rawson Lake watershed, as well as the chemistry of precipitation, streamflow, and the lake are presented. Inputs of water and most chemicals varied by as much as 2 times from one year to the next, illustrating that several years’ data are necessary to determine accurately average nutrient inputs and losses from an ecosystem. Precipitation appeared to be almost the sole source of P and N to lake and terrestrial ecosystems, although N2 fixation cannot be dismissed in the latter case. Significant proportions of Ca, Mg, Na, K, Cl, and SO4 were supplied directly from precipitation. The lake also received substantial quantities of these elements as well as silicon, from weathering of terrestrial geological materials. Although far from any major industrial sources of SO2, the pH of precipitation averaged < 5 for the years studied. Both terrestrial and lake systems retained a high proportion of entering P and N, and smaller proportions of other nutrients. Interpretation of relative retentions of nutrients revealed that the terrestrial ecosystem has well-balanced P and N supplies, while the lake was P limited. Rates of loss of chemicals from the terrestrial watershed of Rawson Lake are comparable to other sites in the Precambrian Shield, but lower than values from other geological settings.

Early posterior ankle release in the treatment of congenital clubfoot

Eighty-one patients (116 clubfeet) underwent posterior ankle release before the age of two years, following unsatisfactory responses to serial corrective casts applied according to the technique of Kite. Seventy-three per cent of these feet showed no or only mild talar flattening at an average follow-up of 7.5 years. Four years, following posterior ankle release there was a none-mild talar flattening rate of 69 per cent in this group compared to a 40 per cent none-mild rate in ankle release reduces the incidence of recurrent equinus deformity and the necessity for subsequent surgery in comparison to the results obtained with serial plaster casts or with tendo Achillis lengthening alone. Recent trends in clubfoot management have favored increasingly early operative intervention. Denham stated that "In the infant hard tissues (bone and cartilage) should be regarded as soft, and the soft tissues (tendon and ligament) as hard." Our operative experience with posterior ankle release supports this philosophy and indicates that early aggressive surgical management is the treatment of choice for the resistant clubfoot.

Cerebro-hepato-renal syndrome of Zellweger. A report of eight cases with comments upon the incidence, the liver lesion, and a fault in pipecolic acid metabolism

Studies of eight patients with this syndrome confirm the characteristic pattern of abnormalities and the autosomal recessive mode of inheritance. The incidence is estimated to be approximately 1 in 100,000 live births. The liver lesion proved to be variable, with features of progressive parenchymal damage rather than a developmental defect of small bile ducts as previously suggested. Elevated levels of pipecolic acid were found in blood and urine and may be related to the basic defect.