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Biomedical subjects

L C Parks

Publications and source records attributed to L C Parks.

At least 19 recordsLinked to original sources
PubMed1979

Membranes of Rhodopseudomonas sphaeroides. VI. Isolation of a fraction enriched in newly synthesized bacteriochlorophyll alpha-protein complexes.

Radioactivity eventually destined for the chromatophore membrane of Rhodopseudomonas sphaeroides was shown in pulse-chase studies to appear first in a distinct pigmented fraction. The material formed an upper pigmented band which sedimented more slowly than chromatophores when cell-free extracts were subjected directly to rate-zone sedimentation on sucrose density gradients. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the purified fraction contained polypeptide bands of the same mobility as light-harvesting bacteriochlorophyll alpha and reaction center-associated protein components of chromatophores; these were superimposed upon cytoplasmic membrane polypeptides. The pulse-chase relation was confined mainly to the polypeptide components of these pigment-protein complexes. It is suggested that the isolated fraction may be derived from sites at which new membrane invagination is initiated.

Bacterial Chromatophores↗
PubMed1978

Membranes of Rhodopseudomonas sphaeroides. V. Identification of bacteriochlorophyll alpha-depleted cytoplasmic membrane in phototrophically grown cells.

The separation of membrane fragments was investigated in extracts of phototropically grown Rhodopseudomonas sphaeroides to determine if the plasma membrane contains discrete regions. A highly purified fraction of bacteriochlorophyll alpha-deficient membrane fragments was isolated by differential centrifugation, chromatography on Sepharose 2B, reaggregation, and isopycnic sedimentation on sucrose gradients. Significant levels of b- and c-type cytochromes and succinate dehydrogenase were demonstrated in the isolated membrane fragments and their appearance in electron micrographs, their polypeptide profile in dodecyl sulfate-polyacrylamide gel electrophoresis, and overall chemical composition were essentially identical to a similar fraction isolated from aerobically grown cells. Their polypeptide profiles were distinct from those of the intracytoplasmic chromatophore and outer membranes, and on the basis of bacteriochlorophyll content the phototrophic fraction was contaminated with chromatophores by less than 9%. The membrane fragments contained no diaminopimelic acid or glucosamine. It is condluded that the membrane fragments isolated from phototrophically growing Rp. sphaeroides have arisen from photosynthetic pigment-depleted regions of the plasma membrane structurally and functionally differentiated from the intracytoplasmic chromatophore membrane. These regions represent conserved chemotrophic cytoplasmic membrane whose synthesis continues under photoheterotrophic conditions.

Aerobiosis↗
PubMed1977

Delayed cutaneous hypersensitivity and human renal allotransplantation.

A group of 154 patients on chronic dialysis has been evaluated by DNCB reactivity. Viewed as a group, these patients exhibit a highly significant decrease in immunologic responsiveness in comparison to normal individuals. However, 19% of patients had an immunologic response to DNCB and 12% an irritant response. This pretransplant DNCB responsiveness correlated significantly with subsequent allograft rejection in 71 renal allotransplant recipients. For example, at 1 year after transplantation graft survival was strikingly different: DNCB- patients, 78%; DNCB+ patients, 29%; and DNCB-IR patients; 20%. Pretransplant recall-antigen testing results in 32 patients did not correlate significantly with subsequent transplant results. Serial posttransplant delayed cutaneous hypersensitivity responses in patients with a positive response to a skin test antigen in the pretransplant period suggest possible usefulness of this technique for detecting rejection in the posttransplant period. DNCB skin testing should be performed in all transplant candidates to evaluate host responsiveness and should aid in future patient management.

Adolescent↗
PubMed1975

Delayed hypersensitivity to DNCB and survival following radiation therapy in patients with solid malignant tumors.

Delayed hypersensitivity to dinitrochlorobenzene (DNCB) was tested prior to radiation therapy in 206 patients with solid tumors. The patients were separated into a DNCB-positive group who showed a significant response to DNCB and a DNCB-negative group who did not. After one year, it was found that patients with a positive DNCB reaction had a statistically better chance of survival than those with a negative DNCB reaction. Although this is not proof that DNCB testing can indicate those patients who should be excluded from radical therapy, it can help identify those who may respond favorably to extended efforts at palliation or cure despite clinically advanced disease.

Adenocarcinoma↗
PubMed1975

Rejection and repair of endothelium in major vessel transplants.

Fresh saphenous vein homografts are gaining popularity as conduits for femoral-popliteal or distal bypass grafts. Aside from major blood group compatibility, there is little clinical evidence that rejection is a significant factor in long-term patency. Some have suggested that blood vessels are weakly antigenic and others indicate that rejection does not endanger long-term patency. Transplantation and toxic damage were produced in experimental animals in order to compare healing processes. Both types of injuries produced early significant endothelial cell proliferation detected by H3-thymidine uptake. This response peaked at 5 days in transplants and ever-expanding islands of proliferating endothelium were present in aortas exposed to 20 percent sodium chloride, leading to healing in 3 to 4 months. In the transplanted vessels, total endothelial destruction occurred at 11 to 28 days, and cells of host origin determined by sex chromatin analysis gradually resurfaced those grafts that maintained patency. At 4 months only two of six carotid artery homografts were patent in unmodified dogs, and eight of nine were patent in animals given 1 mg. per kilogram of Imuran. All patent grafts were resurfaced by host cells. We conclude that rejection does play a role in long-term patency; that donor endothelium of living vascular grafts cannot maintain sufficient proliferative capacity to repair immunological damage; that small doses of Imuran significantly alter the rate of destruction leading to more orderly repair and patency; and that clinical trials utilizing one half the dose of Imuran required for kidney graft survival are likely to improve significantly the long-term patency rate of fresh arterial or venous homografts in man.

Animals↗
PubMed1974

Alpha Fetoprotein: An index of progression or regression of hepatoma, and a target for immunotherapy.

CLINICAL AND LABORATORY STUDIES OF AFP PRODUCING HEPATOMAS DEMONSTRATED THAT: 1) serum AFP levels correlated directly with tumor growth; 2) circulating AFP could be cleared by passive administration of an. excess of anti-AFP; and 3) highly specific anti-AFP functioned as a carrier to localize diagnostic and possibly therapeutic amounts of radioactivity in hepatoma tissue. These studies helped elucidate certain criteria which should be fulfilled before attempts to initiate passive humoral immunotherapy of cancer are undertaken.

Alpha-Globulins↗