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Biomedical subjects

Y Nakagawa

Publications and source records attributed to Y Nakagawa.

At least 19 recordsLinked to original sources
PubMed1979

Transfer of cholesterol between liposomal membranes.

The transfer of cholesterol between liposomal membranes was examined. On incubation of liposomes compsoed of egg yolk phosphatidylcholine, phosphatidic acid and cholesterol (molar percentage, 65.8 : 1.3 : 32.9 or 65.5 : 6.3 : 31.2), almost complete equilibration of the cholesterol pools was achieved within 6 to 8 h at 37 degrees C. The rate of transfer of cholesterol from the liposomes, in which cholesterol was introduced by 'the exchange reaction', was not significantly different from that from liposomes prepared in the presence of cholesterol, in which the cholesterol was distributed homogenously. These findings indicate that half life for 'flip-flop' of cholesterol molecules in egg yolk phosphatidylcholine liposomes is less than 6 h at 37 degrees C. The transfer of cholesterol between liposomes was strongly dependent on temperature and was affected by the fatty acid composition of the phospholipid, suggesting that the 'fluidity' of the membranes strongly influences the transfer rate. A preferential distribution of cholesterol molecules was observed in heterogeneous liposomes with different classes of phospholipids. The 'affinity order' of cholesterol for phospholipid deduced from the present experiments is as follows: beef brain sphingomyelin greater than dipalmitoylglycerophosphocholine = dimyristoylglycerophosphocholine greater than egg yolk phosphatidylcholine.

Cholesterol↗
PubMed1979

Transfer of cholestane spin label between lipid bilayer membranes and its molecular motion in membranes.

The relation between the molecular motion of a steroid in lipid membranes and the transfer rate between membranes was examined using radioactive cholestane spin label. Order parameters of the molecule were determined in bilayers composedof dipalmitoylglycerophosphocholine or egg yolk phosphatidylcholine at various temperatures. The line widths of the ESR signal of the cholestane spin label in membranes, which depend upon the rate of molecular axial rotation in the membranes, were also measured. The temperature dependences of these two parameters and of the transfer rate suggest a close correlation between the rate of molecular axial rotation and the transfer rate.

Cholestanes↗
PubMed1979

Affinity chromatographic purification of papain.

The reinvestigation of the affinity chromatographic method of purifying papain has been carried out. It has been reported that papain could be purified by taking advantage of the affinity of the enzyme for the insolubilized peptide inhibitor, agarose-Gly-Gly-Tyr(Bz)-Arg. Using pure tetrapeptide obtained commercially and standard coupling procedures, a significant purification of papain could not be achieved. Both active and nonactivatible enzyme bound to a column prepared in this manner were eluted together by the use of deionized water. An affinity medium with properties similar to those reported by Blumberg et al. was obtained by removal of the benzyl group on tyrosine prior to coupling with agarose. The deprotected tetrapeptide was also synthesized by an independent route and inhibition constants for the binding of the protected and deprotected tetrapeptide to papain were determined in kinetic experiments.

Amino Acid Sequence↗
PubMed1979

Kinetic studies on enzymatic acetylation of chloramphenicol in Streptococcus faecalis.

The kinetics of chloramphenicol (CP) acetylation by CP acetyltransferase from Streptococcus faecalis was studied. CP was shown to be acetylated enzymatically to its 3-O-acetyl derivative (3-AcCP) in the presence of acetyl coenzyme A, after which 3-AcCP was converted nonenzymatically to its 1-O-acetyl isomer, 1-O-acetyl CP (1-AcCP). At equilibrium, the 1-AcCP and 3-AcCP were present in a 1:4 ratio. Subsequently the diacetylated product, 1,3-O-O-diacetyl CP [1,3-(Ac)2CP], was enzymatically produced from 1-AcCP by the same enzyme. Theoretical calculation of rate constants (k1, k2, k3) for each successive reaction is as follows: (Formula: see text). This calculation gave k1 = 0.4 min-1, k2 = 0.002 min-1, and k3 = 0.016 min-1. Experimental results agreed closely with these calculated values.

Acetylation↗
PubMed1979

Effects of several beta-blocking agents on the development of hypertension in spontaneously hypertensive rats.

Antihypertensive effects of chronic oral administration of adrenergic beta-blocking agents were assessed in SHR. Propranolol, pindolol, oxprenolol, atenolol and labetalol were used as beta-blockers and the effects of these compounds on the blood pressure and the heart rate were compared with those of hydralazine, a representative vasodilating antihypertensive agent. Propranolol, oxprenolol and atenolol produced a definite decrease in the heart rate; the development of hypertension was retarded. Pindolol produced antihypertensive effects only after a longer period of administration and such were associated with insignificant decrease in heart rate. With a shorter period of administration the drug produced only an insignificant fall of blood pressure with practically no change in the heart rate. With labetalol, a beta-blocker with alpha-blocking action, a fall of blood pressure appeared earlier and was of greater magnitude. Hydralazine produced a definite antihypertensive effect, which appeared immediately after administration and was associated with a tachycardia. In pithed rats, only pindolol produced a definite fall of blood pressure. On the basis of these findings, possible mechanisms of antihypertensive effects of beta-blockers were discussed.

Adrenergic beta-Antagonists↗
PubMed1979

Effects of 2-nicotinamidoethyl nitrate on the cardiovascular system.

Using the dog as experimental animal, effects on the cardiovascular system of a new vasodilator, 2-nicotinamidoethyl nitrate (SG-75), were studied. In the heart-lung preparation, the compound produced a dose-dependent increase in the coronary blood flow, which was associated with only a minimal increase in the myocardial oxygen consumption. There was essentially no change in the myocardial function. The myocardial redox potential was shifted to more positive values. In the isolated perfused heart preparation (Langendorff's preparation), SG-75 produced a dilatation of only the small resistive arterioles. However, it produced a dilatation of the large conductive artery in underperfused myocardium. SG-75 produced a significant increase in the cerebral venous outflow, associated with an increase in the cerebro-spinal fluid pressure. It produced a reducation of the venous return, which was especially prominent in the lower half of the body. In the isolated smooth muscle preparation of the coronary artery, high-doses of SG-75 induced calcium antagonistic effects and produced a relaxation of the lanthanum contracture.

Animals↗