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121.
The activation of yeast proteinase B at pH 5 has been suggested to be due to the degradation of a specific inhibitor for the enzyme, IB, by proteinase A. However, we found that when pepstatin, which completely inhibits proteinase A, was included in the pH 5 activation mixture, the same time-dependent activation of proteinase B was observed. Furthermore, proteinase B preparations that were void of proteinase A activity were still activated by incubation at pH 5. We found that the activation of proteinase B at pH 5 was due primarily to the irreversible loss of inhibitory effect of IB, which can be resolved by isoelectrofocusing into four distinct bands with isoelectric points of 4.6, 6.1, 6.8 and 7.6. These four forms of IB showed varying degrees of stability at pH 5, which may explain some of the differing observations reported in the past. 相似文献
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A potent platelet aggregation inducer (platelet aggregoserpentin) was purified from Trimeresurus gramineus snake venom by DEAE-Sephadex A-50 and Sephacryl S-300 column chromatography. It was homogeneous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It elicited dose-dependently platelet aggregation and serotonin release reaction in rabbit platelet-rich plasma and platelet suspension. Exogenous calcium was required for its activity. Creatine phosphate/creatine phosphokinase and apyrase showed no significant inhibitory effect on aggregoserpentin-induced platelet aggregation in platelet suspension. Aggregoserpentin induced aggregation in ADP-refractory platelet-rich plasma. It caused no detectable malonic dialdehyde formation in the process of platelet aggregation. Indomethacin did not inhibit aggregoserpentin-induced platelet aggregation. Mepacrine abolished preferentially its aggregating activity, while prostaglandin E1 completely blocked both aggregoserpentin-induced aggregation and release reaction. Furthermore, platelet aggregoserpentin lowered basal and prostaglandin E1-stimulated cAMP levels in platelet suspension. Nitroprusside inhibited both its aggregating and releasing activity, while verapamil preferentially blocked its aggregating activity. It is concluded that aggregoserpentin activated platelets through lowering cAMP levels or the activation of endogenous phospholipase A2, resulting in the formation of platelet activating factor, but not of prostaglandins. 相似文献
127.
Evaluation of cross-sectional geometry and mass density distributions of humans and laboratory animals using computerized tomography 总被引:1,自引:0,他引:1
The purpose of this study was to determine the cross-sectional geometry and mass density distribution of a young porcine subject using the X-ray computerized tomographic (CT) method and to perform a comparative study of anatomical features of this subject and a 3 yr old female child specimen. The cross-sectional CT scans of the porcine subject were obtained at 1 cm intervals. The outlines of each cross section and of selected anatomical components within each section were obtained by standard picture processing techniques. The mass and inertia tensor for each cross section and for each anatomical structure in a section were computed based on the CT numbers. The porcine subject was then sacrificed, frozen, sectioned and photographed. These sectional photographs were then compared with those obtained from the CT method. Tabulated cross-sectional mass and inertia tensor obtained from CT scans of the porcine subject were also used to compare with similar results derived from previously completed CT scans of the 3 yr old female child specimen. In particular, the comparisons were made on the location of the center of gravity and the inertia tensor in the head, neck, head and neck and cervical spine regions. Some immediate applications of this data are inputs to finite element models, lumped parameter biodynamic models, computer simulation of vehicle crash victims, and dummy design. 相似文献
128.
Abstract: Adenylate cyclase in microvessels isolated from rat cerebral cortex was stimulated by guanine nucleotides, catecholamines, prostaglandin E1 , prostaglandin E2 , and 2-chloroadenosine. Catecholamine stimulation was mediated by interaction with β-adrenergic receptors. The order of relative potency was: isoproterenol > epinephrine > norepinephrine. Activation of microvessel adenylate cyclase by prostaglandins E1 and E2 as well as by 2-chloroadenosine was dose related. Twenty-two peptides were tested for possible effects on the microvessel adenylate cyclase. Only vasoactive intestinal polypeptide (VIP) was stimulatory. No inhibitory action was observed. Activation by VIP required guanosine triphosphate and was dose dependent from 10 n M to μ M (ED50 = 0.1 μ M ). At 30°C, stimulation of adenylate cyclase by the peptide increased linearly with time for up to 15 min. The effect of VIP was not inhibited by phentolamine or propranolol, suggesting that its action was not elicited by interaction with α- or β-adrenergic receptors. Activation achieved by VIP and isoproterenol, prostaglandin E1 , or 2-chloroadenosine was the sum of the individual stimulations, suggesting that receptors for VIP were distinct from those for isoproterenol, prostaglandin E1 , and 2-chloroadenosine. 相似文献
129.
At sites of blood vessel injury, platelets release numerous substances that may have biological activities influencing cellular responses. In this study we examined separately the chemotactic activity for fibroblasts of three highly purified proteins obtained from platelet alpha granules: platelet factor 4 (PF4), platelet-derived growth factor (PDGF), and beta-thromboglobulin (BTG). We observed that each of these proteins was strongly chemotactic for fibroblasts, with maximum chemotactic activity in each instance comparable to that observed with an optimal concentration of the control chemotactic protein, plasma fibronectin. Each protein was active at very low concentrations. The peak chemotactic activities of PF4, PDGF, and BTG occurred at 200 mg/ml, 30 ng/ml, and 6 ng/ml, respectively. Specificity of fibroblast chemotaxis to individual platelet proteins was provided by finding that anti-PF4 immunoglobulin blocked the chemotactic activity of PF4 without affecting the chemotactic activity of PDGF, while anti-PDGF immunoglobulin blocked the activity of PDGF but did not alter the capacity of PF4 to promote fibroblast chemotaxis. These results suggest that in vivo several alpha granule proteins released from platelets may affect wound healing by causing directed fibroblast migration. 相似文献
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