Coronary vascular and myocardial responses to selective hypoxic and/or hypercapnic carotid chemoreceptor stimulation were investigated in constantly ventilated, pentobarbital or urethan-chloralose anesthetized dogs. Bilaterally isolated carotid chemoreceptors were perfused with autologous blood of varying O2 and CO2 tensions via an extracorporeal lung circuit. Systemic gas tensions were unchanged. Effects of carotid chemoreceptor stimulation on coronary vascular resistance, left ventricular dP/dt, and strain-gauge arch output were studied at natural coronary blood flow with the chest closed and during constant-flow perfusion of the left common coronary artery with the chest open. Carotid chemoreceptor stimulation slightly increased left ventricular dP/dt and slightly decreased the strain-gauge arch output, while markedly increasing systemic pressure. Coronary blood flow increased; however, coronary vascular resistance wa.as not affected. These studies show that local carotid body stimulation increases coronary blood flow but has little effect on the myocardium. The increase in coronary blood flow results mainly from an increase in systemic arterial pressure. Thus these data provide little evidence for increased sympathetic activity of the heart during local stimulation of the carotid chemoreceptors with hypoxic and hypercapnic blood.
The distribution of blood flow to the subendocardial, medium and subepicardial layers of the left ventricular free wall was studied in anaesthetized dogs under normoxic (A), hypoxic (B) conditions and under pharmacologically induced (etafenone) coronary vasodilation (C). Regional myocardial blood flow was determined by means of the particle distribution method. In normoxia a transmural gradient of flow was observed, with the subendocardial layers receiving a significantly higher flow rate compared with the subepicardial layers. In hypoxia induced vasodilation this transmural gradient of flow was persistent. In contrast a marked redistribution of regional flow was observed under pharmacologically induced vasodilation. The transmural gradient decreased. In contrast to some findings these experiments demonstrate that a considerable vasodilatory capacity exists in all layers of the myocardium and can be utilized by drugs. The differences observed for the intramural distribution pattern of flow under hypoxia and drug induced vasodilation support the hypothesis that this pattern reflects corresponding gradients of regional myocardial metabolism.
The effect of the major metabolite of aspirin, namely salicylic acid, upon the pentose phosphate pathway (PPP) of normal and G6PD-deficient red cells has been studied. Salicylic acid was shown to inhibit this pathway in proportion to the amount present. At any concentration of this substance there was greater inhibition of the PPP in G6PD-deficient than in normal red cells.
Euglena gracilis contains a protein system which can utilize the reducing power of NADPH in the ribonucleotide reductase-catalyzed reduction of CTP. The proteins required for this reaction are a flavoprotien with a molecular weight of approximately 185,000 which is functionally similar to thioredoxin reductase (NADPH), EC 188.8.131.52, and another protein (Protein I) whose function in the reaction is unknown. This new protein does not appear to contain a prosthetic group and has a molecular weight of approximately 240,000. In addition, the ribonucleotide reductase active in the Euglena NADPH-thioredoxin reductase system is more complex than the protein reported in a previous publication [(1974) j. Biol. Chem. 249, 4428-4434]. The enzyme preparation described in this report contains four different types of polypeptide chains which may complex to form the active enzyme.
Parenteral and oral application of kallikrein (EC 184.108.40.206)--a kinin-releasing proteinase from porcine pancreatic tissue--significantly stimulates quantitative and qualitative sperm motility in subfertile males with semen criteria of asthenozoospermia. Improvement of sperm motility was found to exist for at least 3 months following termination of the 7 week duration kallikrein treatment. Additionally, a significant increase in the number of spermatozoa was observed 3 and 5 months after starting parenteral application of kallikrein.
The localization of the previously postulated interface recognition site (IRS) in porcine pancreatic phospholipase A2, required for a specific interaction between the enzyme and organized lipid-water interfaces, was investigated by ultraviolet difference spectroscopy, by measurements of the intrinsic fluorescence of the unique Trp residue, and by protection experiments against specific tryptic hydrolysis. Using the enzymically nondegradable substrate analogues: CnH(2n+1)(0-)OOCH2CH2N+(CH3)3-(H,OH), it is shown that the rather hydrophobic N-terminal sequence of the enzyme, viz., Ala-Leu-Trp-Gln-Phe-Arg, is directly involved in the interaction with the lipid-water interface. Besides hydrophobic probably also polar interactions contribute to the binding process. At neutral or acidic pH the presence of a salt bridge between the N-terminal alpha-NH3+ group and a negatively charged side chain stablizes the interface recognition site and allows the enzyme to penetrate micellar surfaces, even in the absence of metal ion. At alkaline pH, interaction of the enzyme with micellar interfaces requires the presence of Ca2+ (Ba2+) ions.
A purification procedure for creatine kinase (EC 220.127.116.11) from muscle of the monke35--170 muequiv H+/mg protein per min at 30 degrees C and a yield of approx. 0.5 g/kg muscle. Assuming equilibrium kinetics, synergistic binding of substrates at one catalytic site is found for both the forward and back reactions. Kinetic constants for the binding of each substrate to the free enzyme and the enzyme-second substrate complex are determined and are compared with those for the enzyme from other species. Inhibition by small anions is determined in the presence of different combinations of substrates and products. SO4(2-) inhibits by simple competitive inhibition and probably binds at the site of the transferrable phosphoryl group. Inhibition by NO3-, NO2-, SCN- and Cl- is more complex and these ions are suggested to mimic the transferrable phosphoryl group in a planar transition-state complex. These anions stabilize the dead-end complex, enzyme-creatine-MgADP, which lacks the transferable phosphoryl group. The effects of these anions on the dissociation constants of the enzyme-substrate complexes is reported and is in accord with the above hypothesis. The dead-end complex in the absence of anion does not protect the essential thiol group against inhibition by iodoacetamide. Addition of NO3- or Cl- to the dead-end complex or a substrate equilibrium mixture without anion confers protection. The essential thiol group is inhibited by iodoacetamide at a rate which is essentially independent of pH over the normal stability range of the enzyme. Contrary to our previous report this pH independence is not altered by the presence of dead-end complex, creatine plus MgADP, in the presence or absence of anion or in the presence of a substrate equilibrium mixture. It is inferred that the 'essential' thiol group of the monkey enzyme has essentially the same properties as that of the rabbit enzyme. In consequence, the inferences made about the role of this group based on our previous work on the monkey enzyme are no longer valid. The present findings are compatible with the essential thiol group playing a conformational role in the catalytic process.
Five distinct ester hydrolases (EC 3-1) have been characterized in guinea-pig epidermis. These are carboxylic esterase, acid phosphatase, pyrophosphatase, and arylsulphatase A and B. Their properties are consistent with those of lysosomal enzymes.