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L Marcus

Publications and source records attributed to L Marcus.

32 records · Page 2Linked to original sources
PubMed1970

Correlation of ultrastructure in Azotobacter vinelandii with nitrogen source for growth.

Azotobacter synthesizes an extensive internal membranous nework when grown with air (N(2)), i.e., under conditions when these bacteria fix nitrogen. Very slight quantities of internal membrane, concentrated mainly about the cell periphery, are formed when Azotobacter grows with fixed nitrogen, i.e., ammonia and amino acids. Compared to cells growing with ammonia, cells utilizing atmospheric nitrogen as the sole nitrogen source are smaller in size and volume, grow one-third slower, and lack detectable poly-beta-hydroxybutyrate.

Air↗
PubMed1970

Properties of a soluble nitrogenase in Azotobacter.

A nitrogenase system that remains in the supernatant fluid after centrifuging for 3 hr at 180,000 x g can be extracted from Azotobacter vinelandii by osmotic lysis of the bacteria. This nitrogenase preparation is oxygen-labile and appears to be similar, though not identical, to that obtained from Clostridium pasteurianum. The particulate characteristic and oxygen stability of previously described preparations are likely due to the method of cell disruption, e.g., in the French pressure cell. The data support a nitrogenase model system in the intact cell in which oxygen-labile enzymes are protected from oxygen by the extensive internal membranous system which Azotobacter synthesize only when they fix nitrogen.

Acetylene↗
PubMed1969

Rapid determination by light scattering of growth parameters of Mycoplasma laidlawii in liquid media.

An impediment to progress in the study of the course of growth, the effects of medium components, antibiotics, etc., of Mycoplasma has been the cumbersome methods of growth measurement currently in use. Heretofore, it required the plating of numerous samples during growth, at least in triplicate, after appropriate dilution, followed by a delay of 2 to 3 days before the colonies developed so that counts could be made. We applied the technique of light scattering to measure the growth of Mycoplasma laidlawii in liquid culture continuously in a manner analogous to the use of absorbancy for bacteria. Scattered light measurements precisely paralleled data obtained by the tedious method of plate counts and were available immediately during the development of the culture. The lower limit of sensitivity with the system described is 10(5)Mycoplasma per ml. The presence of serum in the medium lowers sensitivity somewhat. However, concentrations of serum up to 10% are easily tolerated. Higher serum content may require calibration curves. Thus the technique may be used with many pathogens, etc., that require serum to develop. One can easily and rapidly measure differences in growth rates as well as final cell yields during the course of growth, rather than 3 days later, after colonies have developed.

Bacteriological Techniques↗
PubMed1967

Occurrence, isolation, and characterization of polyribosomes in yeast.

This report details the procedural requirements for preparing cell-free extracts of yeast rich in polyribosomes. This enabled us to demonstrate the occurrence of polyribosomes in yeast, to show their role in protein synthesis, and to devise methods for their resolution and isolation. When certain precautions are met (the use of log phase cells, rapidly halting cell growth, gentle methods of disruption, sedimentation through exponential density gradients, etc.), individual polyribosome size classes ranging up to the heptosome can be fractionated and separated from their nearest neighbors. Larger size classes are resolved partially among themselves, free of smaller polyribosomes. This was confirmed by extensive electron micrographic studies of material from the various fractions obtained upon density gradient centrifugation of yeast extracts. Modifications of the gradients and procedure should allow fractionation and isolation of the larger polyribosomes, including those containing polycistronic messages. Yeast polyribosomes are disaggregated to single ribosomes by longer term grinding, cell disruption by the French pressure cell, the Hughes press, or by incubation with dilute RNAse. Yeast polyribosomes are active in the incorporation of amino acids into polypeptide; the single ribosomes exhibit only slight activity. The latter activity is probably due to the presence of a small fraction of monosomes still containing mRNA. Poly-U stimulates amino acid incorporation only in the single ribosomes.

Cell Division↗
PubMedDate not supplied

Extracorporeal removal of mercury by hemoperfusion through agarose-polymercaptal microsphere beads.

Uniform agarose-polymercaptal microsphere beads (APMMB) of 1.0-mm diameter were prepared by encapsulating thousands of polymercaptal microspheres of 0.8-micron average diameter within an agarose matrix. Those beads show a high avidity and affinity for mercury and readily remove mercury compounds bound to serum proteins. In vivo detoxification trials in dosed rabbits and dogs showed the effectiveness of the APMMB for removal of mercury compounds by hemoperfusion. The rate for mercury removal is enhanced by addition of cysteine. The biocompatibility of the APMMB, measured by the depletion of the formed elements and various soluble components of the blood, is also demonstrated.

Animals↗
PubMedDate not supplied

Extracorporeal removal of specific antibodies by hemoperfusion through the immunosorbent agarose-polyacrolein microsphere beads: removal of anti-bovine serum albumin in animals.

We describe the production of a unique immunosorbent system, agarose-polyacrolein microsphere beads (APAMB) for removal of a specific antibody, anti BSA, and its efficacy in animal trials. This is a model system for hemoperfusive removal of specific antibodies or antigens directly from whole blood. The agarose beads (1.0 mm mean diameter) contain thousands of microspheres of 0.2 micron mean diameter. The microspheres which contain the ligand are encapsulated within an agarose matrix to confer physical strength, biocompatibility, spacial configuration, and porosity allowing rapid entry of plasma for reaction. Any antigen may be linked covalently to spacers on the polyacrolein microspheres to remove a specific antibody, or vice versa. Thus the APAMB remove specific molecules in contrast to the charcoal or ion exchange resins currently in use. Removal of antibody is efficient and rapid, therefore, short hemoperfusive times may be used. The beads are biocompatible; there are negligible decreases in RBC, WBC and platelets. Electrolytes and other soluble components also are minimally affected. Therapy, at the least palliative, of autoimmune disorders i.e., multiple myeloma, macroglobinemia, autohemolytic anemias, idiopathic thrombocytopenia, myasthenia gravis, rheumatoid arthritis, thyroiditis, glomerulonephritis, etc, is potentially available with this or its further improved versions.

Acrolein↗
PubMedDate not supplied

Renegotiating health care. Interview by Richard L. Reece.

Richard L. Reece, MD, interviewed Leonard Marcus, PhD, on May 21, 1999, to talk about his book, Renegotiating Healthcare, Resolving Conflict to Build Collaboration, and the Program for Healthcare Negotiation and Conflict Resolution he directs at the Harvard School of Public Health. Dr. Marcus discusses conflict management and negotiation in an industry besieged by change . He says, "we are, in effect, renegotiating the very assumptions and premises that have guided the health care system over the last few decades." In such a turbulent environment, it is crucial that all stakeholders can move to higher ground and resolve their differences instead of escalating the war. The key, Marcus says, is providing options through interest-based negotiation and mediation, so that the parties can look at the bigger picture and reconnect with what they are all committed to accomplishing in health care. While conflict can be destructive, it also can provide opportunities for people to look at where there are problems, to identify and correct those problems, and achieve something even better than what they began with through the process.

Boston↗
PubMedDate not supplied

From soma to psyche: the crucial connection. Part 2. 'Cross-cultural medicine' decoded: learning about 'us' in the act of learning about 'them'.

UNLABELLED: The scorpion's bite--a culturally inept response to a medical emergency. Margaret Clark's criteria--keys to cultural barriers in medical care. Clifford Geertz's injunction: to view the culturally "different" as mirrors of the unacknowledged self. The case of José--scandal of his "compartmentalized" treatment. QUESTION: How much context may a physician be willing to absorb? Shawcross's The Quality of Mercy: western medical teams in Cambodian refugee camps--their good intentions versus their ethnocentric gaffes. The elderly as avatars of a "culture within a culture." Their beliefs, fears, dreams, and intimations--a "terra incognita" for service providers. Sardonic recoil against them (as in Shem's novel House of God) by residents--a professionally sanctioned response, deflecting what might otherwise be unendurable demands on their varied quotas of pity. Sisela Bok's moral claims: (1) for the integrity of decision making among the sick; (2) for the autonomy of the "dying response" among the aged. Steinberg's The Ethnic Myth: indictment of those using cultural difference to "explain" (or rationalize) health--and other--deficits rooted in historic, social, or economic inequity.

Aged↗