The effect of radiations on galactozymase formation in yeast

Stimulation by x-radiation of enzyme induction and growth in Escherichia coli

Escherichia coli B has been grown in a liquid medium containing, besides inorganic salts, glucose and ammonium chloride as sole sources of carbon and nitrogen. The micro-organisms do not grow if maltose is substituted for glucose. Similarly, washed suspensions of Esch. coli which oxidize glucose vigorously have an insignificant O 2 -uptake with maltose. However, maltose is utilized for growth if NH 4 Cl is replaced by glutamic acid. Apparently the bacteria cannot form the enzyme needed to utilize maltose from their existing protein equipment but can if given a suitable organic nitrogen source. X-radiation of 4-8 kr (190 kVp, 10 mA, dose rate 8 kr/min) changes these conditions fundamentally: (i) Washed suspensions of irradiated Esch. coli oxidize glucose as fast as controls, but—unlike the controls—develop an increasing respiration in presence of maltose, the maximal rate (after 4 to 8 kr) being attained within 3 h and approaching that for glucose. (ii) This response to maltose is suppressed by chloramphenicol. (iii) Micro-organisms viable after irradiation can grow on maltose in the liquid medium with NH4Cl, although slowly. (iv) The viable irradiated micro-organisms multiply with maltose and glutamate much faster than unirradiated controls for most of the logarithmic growth phase. This has been confirmed by turbidity measurements and plate counts. (v) The response to maltose is lost on incubation of the bacteria with glucose and NH 4 Cl. (vi) Both controls and irradiated Esch. coli contain maltase. This has been demonstrated with ultrasonically disintegrated bacteria where the addition of maltose and glucose oxidase (notatin) caused an O 2 -uptake at equal rates in both samples. These results and further evidence justify the conclusion that the observed irradiation effects are due to the induction of permease for maltose in irradiated micro-organisms.

Enzyme formation in non-viable cells

An attempt has been made to find conditions which would completely dissociate viability from capacity to synthesize enzymes in yeast cells. The only lethal agent or condition found which yielded complete dissociation was x-irradiation. Dosages leading to 99.9 per cent lethality and greater exhibited no inhibitory action on the capacity of the treated suspensions to synthesize maltozymase and galactozymase. Such suspensions also retained their ability to assimilate externally supplied nitrogen and employ it in the synthesis of enzyme.

Studies on the mechanism of the photosensitized inactivation of E. coli and reactivation phenomenon

In order to find a more satisfactory interpretation of the phenomenon of photosensitized inactivation of bacteria, studies were performed under various experimental conditions on methylene blue and E. coli. In summary the findings are as follow:- 1. The dye is absorbed by the bacteria according to the Langmuir isotherm and can be removed by ionic substitutions; the dye binding to the bacteria is predominantly ionic; the dye-bacteria complex produces a new absorption peak in the 610 mmicro wave length region, and the action spectrum corresponds to the spectral absorption of the dye-bacteria complex. 2. There is an optimum dye concentration range for the photosensitized inactivation. 3. Photosensitized inactivation of bacteria can take place both in the frozen and liquid states and the presence of oxygen is essential to the inactivation process. 4. Hydrogen peroxide, formed by reoxidation of the reduced methylene blue, does not inactivate bacteria. 5. Following the photosensitized inactivation, E. coli lose their ability to reduce the methylene blue in the presence of various hydrogen donors, suggesting that enzymes are involved in the inactivation process. 6. Bacteria inactivated by photosensitization can be reactivated by prolonged storage after irradiation; the recovery rate increases with increasing temperature (maximum 37 degrees ), and is also influenced by the presence of various hydrogen donors. In view of collected experimental data, the basic reaction mechanisms are analyzed in photosensitized inactivation. The first step of the reaction seems to be excitation of the dye-bacteria, or dye-bacteria oxygen complex, by a photon which produces an activated complex. In such a state, molecular oxygen is capable of producing an oxidizing reaction, which results in the inactivation of the bacteria. Some aspects of the detailed reactions taking place at the cell surface are discussed.