ABSTRACT
We showed previously that glucose-6-phosphatase activity was characterised in intact liver microsomes by a hysteretic transition between a rapid and a slower catalytic form of the enzyme. We have now further investigated the substrate specificity of these two kinetic forms. It was found that the pre-incubation of intact microsomes with mannose-6-phosphate or glucose-6-phosphate (50 microM for 30 s) suppressed the burst in glucose-6-phosphatase activity, that the hysteretic transition was reversible and that mannose-6-phosphate inhibited glucose-6-phosphate hydrolysis during the first seconds of incubation, but not anymore after the burst. Our results indicate (i) that mannose-6-phosphate is recognised by the enzyme and can promote the hysteretic transition and (ii) that the transient phase is part of the catalytic mechanism itself.
Subject(s)
Glucose-6-Phosphatase/metabolism , Glucosephosphates/metabolism , Mannosephosphates/metabolism , Animals , Catalysis , Glucose-6-Phosphate , Glucosephosphates/pharmacology , Hydrolysis , Kinetics , Mannosephosphates/pharmacology , Microsomes, Liver/enzymology , Rats , Substrate SpecificityABSTRACT
A simple dilution test for evaluating the individual effect on enzymatic activity of [Ca2+], [EGTA], or [Ca.EGTA] variations in Ca-EGTA buffers is presented. We verified that a 50-fold dilution of the buffer (25-0.5 mM) at constant pH did not affect [Ca2+] (measured with fura-2), whereas [EGTA] and [Ca.EGTA] varied. Therefore the test can be applied to evaluate the proper effect of Ca2+ in a Ca-EGTA buffer on enzyme activity because such an effect is expected to remain unchanged upon dilution of the buffer. Applications of the test are shown for three enzymes apparently sensitive to Ca2+ but found to be effectively influenced only by Ca.EGTA (liver glucose-6-phosphatase), EGTA (intestinal mucosa phosphatase), or indeed Ca2+ (brain cyclic nucleotide phosphodiesterase).
Subject(s)
Calcium/chemistry , Egtazic Acid/chemistry , Enzymes/metabolism , 3',5'-Cyclic-AMP Phosphodiesterases/metabolism , Animals , Brain/enzymology , Buffers , Enzymes/drug effects , Glucose-6-Phosphatase/metabolism , Intestinal Mucosa/enzymology , Liver/enzymology , Phosphoric Monoester Hydrolases/metabolism , RatsABSTRACT
Medical records of 47 dogs with pulmonary thromboembolism were reviewed. Middle-aged to older dogs predominated and dyspnea and arterial hypoxemia were consistent clinical findings. Thoracic radiographic findings were variable. Cardiac disease, neoplasia, hyperadrenocorticism, disseminated intravascular coagulation, and sepsis were identified most frequently. Multiple disease processes were identified in 64% of the dogs.
Subject(s)
Dog Diseases/etiology , Pulmonary Embolism/veterinary , Adrenocortical Hyperfunction/complications , Adrenocortical Hyperfunction/veterinary , Animals , Bacterial Infections/complications , Bacterial Infections/veterinary , Catheters, Indwelling/veterinary , Disseminated Intravascular Coagulation/complications , Disseminated Intravascular Coagulation/veterinary , Dogs , Dyspnea/veterinary , Female , Heart Diseases/complications , Heart Diseases/veterinary , Hypoxia/veterinary , Kidney Diseases/complications , Kidney Diseases/veterinary , Male , Neoplasms/complications , Neoplasms/veterinary , Pulmonary Embolism/complications , Pulmonary Embolism/etiology , Retrospective Studies , Tachycardia/veterinaryABSTRACT
An adult male cat was examined because of chronic respiratory tract disease. Results of thoracic radiography indicated overinflation of the right lung, and atelectasis or agenesis of the left lung. Notable aerosol deposition (ventilation) to the right caudal lung lobe was seen by use of pulmonary ventilation scintigraphy. Postmortem findings suggested the primary pathoanatomic lesion was bronchial dysgenesis involving all but the right caudal lung lobe.
