Role of coenzyme in aminotransferase turnover

The role of coenzyme in determining intracellular contnet of pyridoxal enzymes was assessed by analyzing effects of pyridoxine deficiency on the rapidly degraded, readily dissociable tyrosine aminotransferase (EC 2.6.1.5) and the slowly degraded, nondissociable alanine aminotransferase (EC 2.6.1.2) of rat liver. Synthesis of the tyrosine enzyme was reduced, leading to a decreased amount of this enzyme, much of which was present as active apoenzyme. Synthesis of alanine aminotransferase was unchanged but much of this enzyme was present as an inactive apoenzyme which retained immunological reactivity. Degradation rates of both enzymes (t1/2 about 1.5 h, tyrosine aminotransferase; about 3 days, alanine aminotransferase) were not changed in pyridoxine deficiency. Hence, interaction with coenzyme is not a significant determinant in intracellular degradation of these aminotransferases. Coenzymes dissociation and intracellular stability probably reflect structural features of the proteins which determine both properties.

Prediction of schistosome cercarial shedding with a physiological - time model

While making longitudinal observations on schistosome cercarial shedding, Pitchford and Visser found that there is an annual fluctuation in the minimum time for cercarial development, which is apparently related to temperature (1). Schistosome control strategy could be designed to take advantage of this fluctuation if it were predictable. Inspired by the successes of physiological time models ('heat-unit models') in predicting life-stage durations of various agricultural pests (2,3), we have developed a model of this type for the schistosomes. This model fits the data of Pitchford and Visser quite well. Coupled with recent temperature history and short term temperature forecast, it could be a useful tool for predicting the onset of cercarial shedding.

Cardiac arrest complicating acute myocardial infarction: predictability and prognosis

Eleven percent of 905 consecutive patients with acute myocardial infarction admitted to the coronary care unit at Duke University Medical Center experienced cardiac arrest. Subgroups of patients at high and low risk for cardiac arrest were identified. Cardiac arrest was experienced by 17 percent of patients with signs of heart failure on admission but by only 3 percent of patients without diabetes mellitus, prior myocardial infarction or heart failure by history or on admission. Only 59 percent of patients with cardiac arrest survived hospitalization compared with 88 percent of those without cardiac arrest. Long-term survival for the 765 hospital survivors was significantly greater in the group without than in the group with arrest at each yearly interval from 1 through 5 years; the 2 year survival rate was 50 and 77 percent, respectively, in these two groups. Many of the deaths among the hospital survivors occurred in patients with signs of heart failure during hospitalization. Among 668 hospital survivors who had mild or no heart failure during hospitalization, cardiac arrest continued to be a significant predictor of mortality. The mode of death among hospital survivors did not differ in the groups with and without cardiac arrest; for example, the incidence rate of sudden death in the two groups was 44 and 37 per cent, respectively. In light of recent reports suggesting that the prophylactic use of antiarrhythmic agents can virtually eliminate virtually fibrillation during the hospital phase of acute myocardial infarction, we contend that such use may substantially reduce both long-term and hospital mortality after acute myocardial infarction.

Does coronary surgery prolong life in comparison with medical management?

This analysis attempts to utilize natural history controls to answer the question as to whether coronary surgery prolongs life in comparison to medical management. Selected natural history studies are compared and contrasted in an effort to obtain an average survival curve for patients with coronary artery disease comparable to those presently being operated. The Duke University Medical Center series of concurrent operated and non-operated patients is reviewed to demonstrate the difference of prognosis of patients with coronary artery disease and the complexities involved in answering the question. It is concluded that, on average, coronary surgery does not prolong life in comparison to medical management over the span of 2-5 years. There may be certain higher risk patients whose lives may be prolonged by aortocoronary bypass surgery but more patients and more prolonged follow-up are needed fully to answer the question.

Differential degradation of messenger RNAs in mammalian cells

Through the use of an assay that measures cellular capacity for specific enzyme synthesis, mRNA of alanine aminotransferase (EC 2.6.1.2; L-alanine:2-oxoglutarate aminotransferase) was found to be degraded with a half-life of 12-14 hr in cultured Reuber H-35 cells; mRNA of tyrosine aminotransferase (EC 2.6.1.5; L-tyrosine:2-oxoglutarate aminotransferase) has a half-life of 2 hr in the same cells. Rates of degradation of the mRNAs are the same whether new mRNA accumulation is blocked by removal of the steroid inducer or by inhibition of mRNA synthesis (actinomycin). Cycloheximide inhibits the normally rapid turnover of tyrosine aminotransferase mRNA, but agents such as puromycin and sodium fluoride, which disrupt polysome structure, do not alter the turnover rate of the tyrosine and alanine aminotransferase mRNAs. The tyrosine and alanine aminotransferase mRNAs appear to be translated at equivalent rates. The data suggest that the degradation rate of these two mRNAs is determined by the polynucleotide structure of the mRNA molecules at or near the site for ribosome binding and initiation.

Identification of yeast phase of pathogenic fungi by the specificity of their aminopeptidase(s)

Specificity of aminopeptidase(s) was fluorimetrically determined in the yeast phase of Histoplasma capsulatum, H. duboisii, H. farciminosum, Blastomyces dermatitidis, Paracoccidioides brasiliensis, Candida albicans and Crytococcus neoformans. After individually incubating each of 26 amino acid-beta-naphthylamides with each yeast, the amount of each amino acid-beta-naphthylamide hydrolyzed was determined by measuring the free naphythylamine. This resulted in a reproducible profile of the aminopeptidase(s) for each fungus when medium, growth time, size of inoculum and incubation period were standardized. This technique provided a rapid and specific means of identification and differentiation among these yeasts. Specific amino acids were identified from the profile of each yeast as those rapidly liberated by the aminopeptidase(s) of that yeast. These amino acids delineated the amino acid requirement for the normal growth of each yeast.

An amino acid liquid synthetic medium for the development of mycelial and yeast forms of Candida Albicans

A chemically defined medium composed of 6 amino acids, biotin, inorganic salts and glucose for the growth of yeast and mycelial phases of Candida albicans at 25 degrees C and 37 degrees of C respectively was developed based on the aminopeptidase(s) profile of the fungus. This medium has proved successful in maintaining the growth characteristics of both phases during serial transfers. The relative pathogenicity, virulence, invasiveness and immunogenicity of the yeast and mycelial phases are discussed.

Amino acid synthetic media for fungal pathogens based on aminopeptidase specificities: Histoplasma capsulatum, Blastomyces dermititidis, Paracoccidioides brasiliensis and Cryptococcus neoformans

The development of simple and chemically defined liquid media for Histoplasma capsulatum, Blastomyces dermatitidis, Paracoccidioides brasiliensis and Crypto-occus neoformans according to their aminopeptidases profiles as amino acid requirement was described. When 1.5% purified agar was added, these media also supported excellent mycelial growth and sporulation of the deep mycoses. H. capsulatum was converted to and maintained in yeast phase when 0.1% L-cystine was added to the solid medium incubated at 37 degrees C.

Degradation of messenger RNA in mammalian cells

Analyses of the response of hydrocortisone-induced tyrosine transaminase in cultured H-35 cells to inhibitors of translation (cycloheximide, puromycin) suggest: (1) that bound ribosomes stabilize messenger RNA in vivo; (2) that messenger is degraded at a rate determined by the rate of translation. Since specific messenger RNAs of mammalian cells are degraded at quite different rates, there may be extensive heterogeneity either in the rate at which ribosomes traverse different messengers or in the number of ribosomes which translate specific messenger RNAs.

Assessment of hormone action in cultured cells

Corticosteroids effect a rapid and marked increase in the enzyme tyrosine transaminase in cultured cells of the Reuber or H-35 hepatoma. This change is comparable in all essential aspects to changes in the livers of rats treated with the same hormones. Methods of cell culture and of biochemical analysis designed to determine the mechanism of steroid action on cultured cells are described.