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Biomedical subjects

B C Johnson

Publications and source records attributed to B C Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1979

Unique amanitin resistance of RNA synthesis in isolated nuclei from Amanita species accumulating amanitins.

In order to understand the basis upon which amanitin-accumulating species of Amanita are able to develop in the presence of these specific inhibitors of RNA synthesis, the in vitro RNA synthesizing activities of nuclei isolated from amanitin-accumulating species. Amanita hygroscopica (culture, derived from amanitin-accumulating carpophore) and A. suballiacea (carpophore), and from the non-accumulating species A. solitaria (culture) and A. brunnescens (carpophore) were tested for their sensitivities to alpha-amanitin inhibition. The nuclear RNA synthesizing activities obtained from both carpophores and cultures of non-accumulating organisms displayed significant sensitivities to alpha-amanitin, whereas those obtained from accumulating organisms displayed remarkable resistance to alpha-amanitin. The observed relationship between levels of amanitins in carpophores and resistance of the RNA synthesizing activities to inhibition by alpha-amanitin supports the hypothesis that amanitins may function as regulators of mRNA transcription in Amanita species.

Agaricales↗
PubMed1976

Soluble enzyme system for vitamin K-dependent carboxylation.

The vitamin K-dependent carboxylating system has been solubilized by Lubrol PX or Triton X-100 treatment of vitamin K-deficient rat liver microsomes. As obtained from vitamin K-deficient rat liver, this soluble preparation is dependent upon the in vitro addition of vitamin K1 for carboxylating activity. The enzyme system is complex and is dependent upon NADH and dithiothreitol for maximum activity. While detergents used to solubilize the enzyme complex do markedly inhibit the activity of the system, the solubilized system is still highly responsive to vitamin K addition and can be used for further study of the carboxylating enzyme system. The requirement for dithiothreitol and the inhibition by p-hydroxymercuribenzoate indicate the involvement of an --SH enzyme in the carboxylating system.

Animals↗
PubMed1976

President's Page.

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Journal Article↗
PubMed1975

Partial purification and characterization of the enzyme which converts precursor liver protein to factor X.

A rat liver post-microsomal supernatant enzyme, which carries out an epigenetic conversion of a protein contained in liver microsomes to Factor X, has been partially purified 250-fold in 50% yield by a combination of salt fractionation and gel filtration. The crude enzyme is stable to freezing and thawing but unstable at 4 degrees C. However, the partially purified enzyme is more stable at 4 degrees C. It requires Ca2+ and HCO3 minus for optimum formation of Factor X activity. The supernatant enzyme is vitamin K dependent and exhibits its maximum rate of formation of Factor X between pH 8 and 8.5.

Animals↗
PubMed1975

Effect of dietary fat and sucrose on the activities of several rat hepatic enzymes and their diurnal response to a meal.

Regulation of the cytoplasmic enzymes, pyruvate kinase (PK), glucokinase (GK), phosphoenolpy ruvate carboxykinase (PEPCK), fructose-1,6-diphosphatase (FDP), ATP citrate-lyase (ATP-CL), NAD-malate dehydrogenase (NAD-MD), NADP-malate dehydrogenase (NADP-MD), glutamic-pyruvic transaminase (GPT), glucose-6-phosphate dehydrogenase (G6PD), and 6-phosphogluconate dehydrogenase (6PGD), in rat liver by dietary fat (F diet) and dietary sucrose (S diet) was investigated. Mealfeeding the S diet to adult rats for 5 and 9 months resulted in a diurnal dietary response (i.e., food response) variation of FDP, GK, ATP-CL, 6PGD, and PK, while meal-feeding the S diet to young rats resulted in diurnal dietary response variation of ATP-CL, G6PD, NADP-MD, 6PGD, GPT, and PK. Meal-feeding the fat diet results in essentially no diurnal variation in enzyme activity. The overall effect of meal-feeding, as compared with ad libitum feeding, of the S diet was to increase the levels of G6PD, ATP-CL, and NADP-MD and to decrease the level of PEck in the meal-fed rats. Young rats meal-fed the two diets have higher enzyme activities than meal-fed adult rats for the observed enzymes (except for GPT and NAD-MD). In general, hepatic levels of the enzymes studied are low in the F diet-fed animals and markedly higher for the S diet-fed animals. These results suggest that dietary carbohydrate specifically induces those enzymes involved in carbohydrate metabolism, whereas dietary fat does not affect their levels. On the basis of prior evidence for an early requirement of RNA synthesis for sucrose induction of G6PD, this widespread induction of liver enzymes by carbohydrate must indicate either increased synthesis of ribosomal RNA with later regulation of synthesis specifically of these enzymes or increased synthesis of a rather large group of specific messenger RNAs i.e., coordinate genetic control of a number of these enzyme messenger RNAs.

Age Factors↗
PubMed1975

Regulation of glucose-6 phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in the meal-fed rat.

Meal-feeding of a high sucrose diet produces a diurnal cycle (i.e., food response) in glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) levels resulting in an elevated level of these enzymes at approximately 12 hours after the start of a 2-hour meal and a return to base level by 24 hours. The effects of actinomycin D and cycloheximide on the 12-hour increases in G6PD and 6GPD were determined. Cycloheximide completely blocked the increase in G6PD if administered 2 or 4 hours after start of the meal, while actinomycin D completely blocked the increase in G6PD if administered at 2 hours and almost completely at 4 hours after start of the meal. These results were obtained previously with starved rats refed a sucrose diet. The diurnal increases in G6PD and 6PGD in meal-fed rats and the induction of G6PD in starved-refed rats thus appear to be regulated by the same mechanism requires RNA synthesis within 4 hours after start of re-feeding. The response of 6PGD to cycloheximide and to actinomycin D at 2 or 4 hours after start of the meal is essentially the same as that of G6PD. These data suggest that the increases in G6PD and 6PGD (and other enzymes) brought about by carbohydrate refeeding AFTER starvation or by carbohydrate meal-feeding on a diurnal cycle are mediated by a rapid change in RNA synthesis. This appears most compatible with a coordinate control of gene expression through messenger RNA synthesis.

Animal Nutritional Physiological Phenomena↗
PubMed1975

President's page.

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Libraries, Medical↗