Pulmonary angiotensin-converting enzyme substrate hydrolysis during exercise.

We examined exercise-induced changes in indicator-dilution estimates of the angiotensin-converting enzyme first-order kinetic parameter, the ratio of a normalized maximal enzymatic conversion rate to the Michaelis constant (Amax/Km), which, under stable enzymatic conditions, will vary with the pulmonary vascular surface area accessible to vascular substrate, the extravascular lung water (an index of the proportion of lung tissue perfused), and the central blood volume (from pulmonary trunk to aorta). Experiments were performed in 10 mongrel dogs at rest and through two increasing levels of treadmill exercise, with the use of two vascular space tracers (labeled erythrocytes and albumin), a water space tracer ([1,8-14C]-octanediol), and a vascular endothelium surface area marker, benzoyl-Phe-Gly-Pro ([3H]BPGP), which is a pharmacologically inactive angiotensin-converting enzyme substrate. The exercise-induced increase in cardiac output was accompanied by a linear increase in central blood volume, and dilutional extravascular lung water rapidly increased to an asymptotic proportion close to 100% of postmortem vascular lung water. There was an average 55% [3H]BPGP hydrolysis, which did not vary with flow, and the computed Amax/Km increased linearly with exercise. We conclude that exercise results in complete lung tissue recruitment and increases the pulmonary vascular surface area available for BPGP hydrolysis linearly with flow, so that pulmonary vascular recruitment continues after full tissue recruitment.     

MAXAMIZE. A DNA sequencing strategy advisor.

The MAXAMIZE advisory system determines from user-provided restriction maps an optimal strategy to do nucleotide sequencing by methods involving end-labeled fragments. The maps may be either simple linear restriction maps of fragments or complex circular maps including restriction sites of a vector. The whole system is interactive and is written in the Genetic English language provided by the GENESIS System, a molecular genetics knowledge representation and manipulation package. In addition, MAXAMIZE provides bookkeeping facilities for sequencing and offers advise on how to verify the newly obtained sequence data.     

Sensitization of lymphocytes against pooled allogeneic cells. II. Characterization of effector cells cytotoxic for autologous lymphoblastoid cell lines

Stimulation of human lymphocytes in mixed leukocyte culture (MLC) with x-irradiated pooled allogeneic normal cells (poolx) was previously shown to result in generation of effector cells cytotoxic for autologous Epstein-Barr virus- (EBV) transformed lymphoblastoid cell lines (LCL). This study was undertaken to determine whether lysis of the autologous EBV- transformed LCL cells by pool-stimulated cells is mediated by cytotoxic Tc lymphocytes (Tc) or natural killer- (NK) like cells, both of which are generated in MLC. In the first series of experiments, proliferating cells were eliminated by treatment of pool-stimulated cells with 5 X 10(-5) M 5-bromodeoxyuridine (BUdR) and light. The remaining cells failed to lyse allogeneic normal lymphocytes and autologous LCL cells, whereas cytotoxicity against NK-sensitive K562 leukemia cells was retained. In the second series of experiments, pool-stimulated effector cells were treated with monoclonal anti-human Tc cell antibodies, OKT3 or OKT8, and complement (C). The cells recovered after antibody and C treatment were diminished in their ability to lyse allogeneic normal lymphocytes as well as autologous LCL cells, whereas their cytotoxicity against K562 leukemia cells was unaffected. These combined results provide strong evidence that lysis of autologous LCL cells by lymphocytes stimulated with pooled allogeneic normal cells is mediated by Tc rather than NK-like cells.     

Human placental N-acetyl-beta-D-hexosaminidase isozymes. Activity toward native hyaluronic acid.

The activity of purified human hexosaminidases A and B toward hyaluronic acid (HA) isolated from cultured human skin fibroblasts was investigated. The cleavage of N-acetylglucosaminyl residues to monosaccharide N-acetylglucosamines by hexosaminidase isozymes was determined in the presence and absence of purified human β-glucuronidase. The pH optima of this reaction, with and without β-glucuronidase, were 4.5 for hexosaminidase A and 4.0 for hexosaminidase B. The hydrolysis of HA by both hexosaminidase isozymes proceeds linearily for at least 18 h in the presence of β-glucuronidase. Concentrations of 0.5–5 units of either isozyme showed a linear relationship with rate of hydrolysis. Without β-glucuronidase, hexosaminidase only cleaved the terminal N-acetylglucosamine residue. However, under optimal conditions, with β-glucuronidase, the hydrolytic activity of hexosaminidase B was about 30% as efficient as that of hexosaminidase A. Approximately 70% of the HA could be degraded by 5 units of hexosaminidase A in the presence of 0.5 unit of β-glucuronidase, as opposed to 25% degraded by hexosaminidase B. These results probably reflect intrinsic differences in the activities of the two isozymes. Since the substrate (HA) did not inhibit the hydrolysis of a synthetic substrate (4-methylumbelliferyl-β-glucosaminide) by hexosaminidase B, the linear kinetics of HA hydrolysis implies no product inhibition. These data indicate that native HA can be hydrolyzed by the combined activities of β-glucuronidase with hexosaminidase A or hexoaminidase B.     

Differential scanning calorimetry of dipalmitoyl phosphatidylcholine analogues and of their interaction products with basic polypeptides

The thermotropic behaviour of dipalmitoyl phosphatidylcholine analogues with a varying number (n) of CH₂ groups between the phosphate and the quaternary ammonium has been investigated. The temperature (T_m) and the enthalphy (ΔH) of the phase transition are non-monotonous functions of the number of CH₂ groups. T_m oscillates between 40 and 45°C and ΔH between 7 and 13 kcal/mol for a variation of n between 2 and 11.It is concluded that the hydrocarbon chains in the head groups do not penetrate the hydrocarbon region and do not contribute directly to the melting of the acyl chains. It is suggested that their length may affect the critical ballance between the attractive and the repulsive forces within the bidimensional lattice of the head groups.Copolypeptides of lysine with phenylalanine do not appreciably affect the T_m but have a pronounced effect on ΔH of the lipid phase transition, which depends strongly on the ratio of the two amino acids in the polypeptide. The effect of copolypeptide of any defined composition on ΔH is also a non-monotonous function of the number of CH₂ groups in the phosphatidylcholine head group, but it does not parallel completely the oscilations in the T_m and ΔH of the pure lipids.     

Thymic function in NZB mice. II. Regulatory influence of a circulating thymic factor on antibody production against polyvinylpyrrolidone in NZB mice.

Administration of a circulating thymic factor isolated from normal pig blood prevented the development of the exaggerated production of anti-polyvinyl pyrrolidone (PVP) antibody in young NZB mice. However, treatment was ineffective if initiated after the 4th week of life at a time when endogenous serum thymic factor (TF) normally disappears in these mice. These data suggest that circulating TF is necessary for the survival of short-lived suppressor T cells normally implicated in the regulation of the production of antibodies against PVP, a thymus-independent antigen. In older NZB mice, TF treatment increased paradoxically anti-PVP antibody production, which suggests that "amplifier" T cell activity could also be under TF influence.     

Inhibition of Microbial Growth by Fatty Amine Catalysts from Polyurethane Foam Test Tube Plugs

When polyurethane foam test tube plugs are autoclaved, they release volatile fatty amines that inhibit the growth of some microorganisms. The chemical structures of these amines were determined by the use of a gas chromatographmass spectrometer. They are catalysts used to produce the foam. The problem of contaminating growth media with toxic substances released from polymeric materials is discussed.