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Biomedical subjects

K Johnson

Publications and source records attributed to K Johnson.

At least 451 records · Page 25Linked to original sources
PubMed1985

Specific transcription of orthopox virus DNA by HeLa cell RNA polymerase II.

A HeLa cell extract was used to transcribe DNA isolated from cowpox virus. Truncated templates generate accurately initiated run-off transcripts of discrete sizes and whose sensitivity to inhibition by alpha-amanitin indicates synthesis by cell RNA polymerase II. A mapped restriction fragment of wild-type cowpox DNA contains specific sites of initiation which are not detected in the geographically equivalent fragment from a cowpox mutant having a defined sequence rearrangement in this region.

Amanitins↗
PubMed1985

Characterization of the bovine lens plasma membrane substrates for cAMP-dependent protein kinase.

cAMP-dependent protein kinase, derived from either calf lens or bovine heart, promotes the phosphorylation of three lens plasma membrane proteins of molecular mass 28 kDa, 26 kDa and 18 kDa. Correlation of the maximal level of phosphorylation of these components with the Coomassie blue staining intensity of fractionated lens membranes suggests that the phosphorylation of the 28 kDa and 18 kDa components may be approximately stoichiometric. The protein kinase substrates could be dephosphorylated by a cardiac sarcoplasmic-reticulum-bound protein phosphatase activity. The 26 k Da component comigrated with MP26, the major lens membrane component that has been localized to the lens fiber cell junction. Treatment of phosphorylated lens membranes with chymotrypsin did not suggest that any of the three major phosphorylated components was derived from the partial proteolysis of a larger phosphoprotein. After electrophoretic separation of phosphorylated proteins, treatment with N-chlorosuccinimide confirmed that there was little similarity in the structure of the three phosphoproteins. Chymotrypsin did, however, reveal a cryptic phosphorylation site in a 22 kDa fragment that appeared to be derived from MP26. Treatment of phosphorylated membranes with reducing agents resulted in the disappearance of the 28 kDa phosphorylated component and the appearance of a new phosphorylated component of 18 kDa; neither MP26 nor the original 18 kDa component was affected by such treatment. It is not clear whether the original 18 kDa phosphoprotein, present in unreduced samples, is the same as that generated with reducing agents from the 28 kDa phosphorylated lens membrane component.

Animals↗
PubMed1985

Simultaneous reticulocyte and platelet counting on a clinical flow cytometer.

Laser flow cytometric analysis is well suited to many clinical immunofluorescent and hematologic applications. One of these is automated reticulocyte and platelet enumerations. We have performed a clinical evaluation of a fluorescence laser flow cytometer reticulocyte and platelet enumeration method using the fluorochrome acridine orange. One hundred and thirty-two clinical specimens from inpatients in our comprehensive cancer center were analyzed for platelet counts and 101 samples from the same population were analyzed for reticulocyte counts by the flow cytometer and simultaneously by conventional techniques. Both the reticulocyte and platelet enumerations achieved a high degree of correlation with standard methods for the nonbone marrow-transplant patients studied (R = .989 for reticulocytes and R = .995 for platelets). Marrow transplant patients had a slightly poorer correlation coefficient for the reticulocyte enumeration (R = .923), but analysis of serial determinations of these patients' samples for reticulocyte counts revealed that results were more consistent over time with the automated method than with the traditional manual method. The laser flow cytometer fluorescence reticulocyte and platelet enumeration methods described are efficient, rapid, and reliable for platelet and reticulocyte counting.

Acridine Orange↗
PubMed1985

Solution kinetics of a water-soluble hydrocortisone prodrug: hydrocortisone-21-lysinate.

Hydrocortisone-21-lysinate was synthesized as an amino acid prodrug of hydrocortisone to serve as a substrate for brush border aminopeptidases. This strategy was developed to demonstrate that an improvement in oral absorption could be obtained through reconversion in vivo. The aqueous stability of hydrocortisone-21-lysinate was studied over the pH range 3-8 at 25 degrees C. Reversible acyl migration of the lysine group between the 21- and 17-position hydroxyl groups was observed as well as hydrolysis. The observed half-life for direct hydrolysis of hydrocortisone-21-lysinate is 40 d at pH 3 and 30 min at pH 7. The relative instability at pH 7 is probably due to electrostatic stabilization of the negatively charged tetrahedral intermediate by the protonated amino groups.

Chromatography, High Pressure Liquid↗
PubMed1985

HPLC determination of clenbuterol in pharmaceutical gel formulations.

A quick, accurate, reproducible high performance liquid chromatographic (HPLC) method for the determination of clenbuterol in the presence of some common pharmaceutical preservatives (i.e., methyl and propyl paraben) is described. The method is specific enough to separate and determine clenbuterol in the presence of degradation products of the formulation components. Extraction of interfering formulation components provides the necessary clean-up to determine clenbuterol via HPLC.

Chromatography, High Pressure Liquid↗
PubMed1985

Spectrum of Kaposi's sarcoma in the epidemic of AIDS.

Kaposi's sarcoma (KS) is seen with increased frequency in the course of the epidemic of acquired immune deficiency syndrome. In this population, KS has manifested in an aggressive and more disseminated fashion as compared to the classical type. As the epidemic of acquired immune deficiency syndrome continues to spread and more cases of KS are evaluated, a distinct diversity in the clinical presentation and in the course of the disease as well as in variation in the prognosis and response to therapy is being observed. A preliminary description of the spectrum of KS in the epidemic of acquired immune deficiency syndrome is presented here.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Proton therapy at Harvard.

Fractionated precision high-dose proton radiotherapy has been carried out at the Harvard Cyclotron Laboratory (HCL) since 1973, in a collaborative effort with the Radiation Medicine Department of Massachusetts General Hospital (MGH) and the Retina Service of the Massachusetts Eye and Ear Infirmary (MEEI). This paper will discuss proton treatment in general, treatment planning procedures, and results to date in major patient categories. 846 patients have been treated with fractionated proton therapy at the Harvard Cyclotron, with normal tissue and tumor responses consistent with an RBE of 1.1 for the proton beam. Proton beam therapy is the treatment of choice for patients with uveal melanomas, and chordomas and chondrosarcomas involving the skull base and cervical spine. Improved dose distribution possible with protons have allowed greater doses than are given conventionally to be delivered to patients with prostatic carcinoma, head and neck malignancies, ano-rectal cancers, and retroperitoneal tumors. Doses employed have been usually 10 to 20% greater than normally would be delivered in our department to such tumors. Generally, local control rates have been good.

Animals↗