Measurement of enzyme reaction rates using advanced pH control system: application of repetitive PF system

The aim of this article is to develop the on-line measurement system of enzyme reaction rates, using an advanced pH controller, which is called a repetitive PF(Programmed Controller/Feedback Compensator) System. In the esterolysis reaction of the N-acetyltyrosine ethyl ester by alpha-chymotrypsin, the enzyme reaction rate could be calculated from the amount of base required for keeping the pH constant. The proposed controller has a learning mechanism in which the knowledge is obtained from the former results of the repetition, and pH was controlled much more successfully by the proposed repetitive PF System than by the conventional on-off controller, PI controller, and the adaptive controller. The enzyme reaction rate could be evaluated each time as accurately as possible based on the result of the controlled batch reaction. Using Lineweaver-Burk plots of the estimated reaction rates, kinetic parameters, such as the enzyme activity and Michaelis-Menten constant, could be estimated more accurately and from fewer experiments by the repetitive PF system than by initial reaction rates using on-off pH-stat.     

Characterization of fractionated polyclonal antibodies for immunoaffinity chromatography

Polyclonal anti-BSA antibodies were ractionated by stepwise elution from an immobilized BSA column by decreasing pH or increasing the concentration of NaSCN. The binding affinities of each fraction and original globulin under physiological conditions and their dependence on pH and ionic environments were compared. Fractions with high association constant under physiological conditions did not necessarily show antigen binding affinity over a wide pH range, but they retained a high affinity at higher ionic strength of NaSCN. Consequently, by combining these two fractionation procedures, a fraction with high affinity and which dissociated at moderate pH was obtained. It is clear that high affinity is not always incompatible with ease of dissociation accompanying a change in conditions.     

Organization of fusicoccin receptor in higher plant plasma membrane: relationship between affinity and molecular mass

Higher plant plasma membranes carry receptors of different affinity for the phytotoxin fusicoccin. Reception of fusicoccin involves proteins belonging to the highly conserved 14-3-3 family, but the complete structure of the fusicoccin receptor (FCR) is unknown. Using radiation inactivation analysis, we estimated the molecular masses of low-affinity and high-affinity FCR at 63 +/- 7 and 130 +/- 15 kD, respectively. The dose dependences of receptor inactivation indicate that microsomal specimens contain "silent" FCRs of 420 +/- 90 kD in amounts commensurate with that of the active FCRs. Both low- and high-affinity FCRs are inactivated by hydrolytic enzymes from the outer surface of the plasma membrane, and impairment of protoplast integrity causes an irreversible transition of the low-affinity binding site into the high-affinity one. A scheme is proposed for the organization of different types of FCR in the plasma membrane, implying that the membrane affinity for fusicoccin reflects the interaction between proteins in the FCR complex.     

NaCl-preferring NZB/B1NJ mice and NaCl-avoiding CBA/J mice have similar amiloride inhibition of chorda tympani responses to NaCl

Integrated chorda tympani nerve responses to NaCl were studied in two mouse strains, an NaCl-preferring NZB/B1NJ and an NaCl-avoiding CBA/J. The NaCl responses of both strains had similar magnitude and were suppressed by amiloride to a similar extent. This suggests that peripheral gustatory responsiveness to NaCl is not the only mechanism underlying mouse strain variation in NaCl acceptance.      

Regulation of the slow Ca++ channels of myocardial cells

Contraction of the heart is regulated by a number of mechanisms, such as neurotransmitters, hormones, autacoids, pH, intracellular ATP, and Ca⁺⁺ ions. These actions are mediated, at least in part, by actions on the sarcolemmal slow (L-type) Ca⁺⁺ channels, exerted directly or indirectly. The major mechanisms for the regulation of the slow Ca⁺⁺ channels of myocardial cells includes the following. cAMP/PK-A phosphorylation stimulates the slow Ca` channel activity, whereas cGMP/PK-G phosphorylation inhibits. DAG/PK-C phosphorylation and tyrosine kinase phosphorylation are suggested to stimulate the slow Ca⁺⁺ channel activity. Intracellular application of G_s protein increases the slow Ca⁺⁺ currents (ICa(L)). Lowering of intracellular ATP inhibits I_Ca(L). Acidosis and increase in [Ca]_i inhibits I_Ca(L). A number of changes in the Ca⁺⁺ channels also occur during development and aging. Thus, it appears that the slow Ca⁺⁺ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of extrinsic and intrinsic factors, and thereby control can be exercised over the force of contraction of the heart.     

Thromboxane A2/endoperoxide receptors mediate cholinergic constriction of rabbit lung microvessels.

Using an X-ray television system, we directly measured the internal diameter (ID; 100-1,000 microns) of small pulmonary arteries and analyzed the effects of cyclooxygenase inhibition and thromboxane A2/prostaglandin endoperoxide (TP) receptor blockade on the ID reductions in response to vagal nerve stimulation (VNS; 16 Hz) and injection of acetylcholine (ACh; 0.3 micrograms) in anesthetized rabbits. The ID reductions of the small arteries in response to VNS and ACh were completely abolished by pretreatment with cyclooxygenase inhibitors indomethacin and meclofenamate. Those reductions were also eliminated by pretreatment with TP receptor antagonists AA-2414 and Ono 3708. Both TP receptor antagonists abolished the ID reduction to thromboxane A2 mimetic U-46619 but did not affect the reduction to norepinephrine. The ID reductions in response to VNS and ACh were eliminated by atropine. The reduction in response to VNS was abolished by hexamethonium bromide, whereas the reduction in response to ACh was not altered by hexamethonium bromide. The results indicate that vasoconstrictions of the rabbit small pulmonary arteries in response to VNS and exogenous ACh are mediated by TP receptors as well as muscarinic receptors. The data suggest that during VNS endogenous ACh acts on muscarinic receptors to constrict the small arteries mainly by generating thromboxane A2 or prostaglandin endoperoxide.     

Diffusive and hydraulic transfer of solutes through homogeneous membranes

Rates of hydraulic transport of water, solute permeabilities, and sieving coefficients of homogeneous kappa-carrageenan and bovine serum albumin membranes were measured. These values increased with the water content of membranes. The data show good agreement with the predictions based on the pore model.     

INDUCTION OF ERYTHROID MATURATION BY DIMETHYL SULFOXIDE IN FRIEND LEUKEMIC CELLS

Enhancement of the erythroid maturation in Friend virus-induced leukemic cells has been examined in vitro by the treatment with dimethyl sulfoxide (DMSO). Although the cell growth was inhibited in the medium containing 2% DMSO, many cells remained viable for a week. By the 3rd day of the culture, the cells treated with DMSO became more strongly agglutinated by phytohemagglutinin than the cells incubated without DMSO. Mouse erythrocyte membrane-specific antigens were also detectable at the 4th day. At the 8th day of the culture hemoglobin synthesis was apparently demonstrated in the cells treated with DMSO, which could not be seen in the untreated cells. Maturation or differentiation along the erythroid pathway in Friend leukemic cells by DMSO is discussed on these markers.