REVERSIBLE DEACTIVATION OF NEUROSPORA ASCOSPORES BY LOW TEMPERATURE

Sun, Clare Y., and Alfred S. Sussman. (U. Michigan, Ann Arbor.) Reversible deactivation of Neurospora ascospores by low temperature. Amer. Jour. Bot. 47(7): 589-593. Illus. 1960.—Heat-activated ascospores of Neurospora tetrasperma are reversibly deactivated after incubation at 4°C. for 36–48 hr. Two cycles of deactivation and reactivation are possible although the percentage germination decreases in the last cycle. By contrast, spores held at 20°C., or in glycerol at 4°C., will remain activated for much longer periods of time. If an incubation period at 20°C. greater than 30 min. is interposed before the activated spores are placed at 4°C., germination occurs despite the cold-treatment. Furfural-activated ascospores, when held at 4°C., are deactivated but can be reactivated only by heat, pointing up a difference between ascospores activated by these different means. Although a fraction of the stimulus afforded by heat-sensitization to chemical activators is preserved for 2 days at —20°C., it is dissipated completely after a short time at 4°C. These data are discussed on the basis of the suggestion that the reversible production of a substance initiates a series of steps which lead to germination. Thus, the temperature minimum of the forward reaction is greater than 4°C. whereas the back reaction proceeds at this temperature.     

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Destruction of Various Kinds of Mycobacteria in Milk by Pasteurization

Various strains of unclassified mycobacteria, Mycobacterium tuberculosis (including H37Rv strains), M. bovis, M. avium, M. fortuitum, and bacille Calmette-Guerin, were exposed to the temperature and time of pasteurization in skim milk in test tubes. Of the 195 strains tested, there were a few surviving colonies among 6 of 33 skotochromogens, 1 of 26 photochromogens, 10 of 79 nonchromogens, and 1 of 9 rapid growers. Subcultures of the surviving colonies failed to resist the pasteurization tests on subsequent trials.     

Properties of steroid sulphatase and arylsulphatase activities of human placenta

1. The properties of enzyme activities hydrolysing the sulphate esters of dehydroepiandrosterone, oestrone and p-nitrophenol are reported. The preparation studied was obtained from the microsomal fraction of human placenta by ultrasonic treatment and addition of Triton X-100. 2. The behaviour of the preparation during sedimentation at 105000g and attempts at purification indicated that the activities were particulate. Electron microscopy demonstrated the rupture of vesicular structures approx. 0.5mu in diameter concurrent with the release of activity. 3. The three activities were always associated throughout repeated attempts at separation by sucrose-density-gradient centrifugation and Sephadex-gel filtration. On the basis of kinetic studies, stability studies and treatment with butanol and ribonuclease it was concluded that a separate enzyme is responsible for each of the three activities. Widely varying plots of activity as a function of pH were consistent with this conclusion. 4. On the basis of sensitivity of the enzymes hydrolysing dehydroepiandrosterone sulphate and oestrone sulphate to ribonuclease and sensitivity of all three enzymes to lipase, it was concluded that the three enzymes are bound to a particle containing lipid and RNA. Enzymic activity is dependent on structural integrity of the particle. 5. A spectrophotometric method for the assay of oestrone sulphate hydrolysis is described. 6. Hydrolysis of nitrocatechol sulphate by human placenta under conditions described for arylsulphatases A and B is reported.