Response of ad-2 mutants of Saccharomyces cerevisiae to carbon dioxide

Summary Confirmation that the ad-2 locus of yeast controls the carboxylation of aminoimidazole ribonucleotide (AIR) to 5-amino-4-imidazole carboxylate ribonucleotide (CAIR) is provided by the observation that 21 out of a sample of 113 ad-2 mutants were affected by CO₂. 19 of the mutants were stimulated by CO₂ and 2 were inhibited. The majority of the CO₂-stimulated mutants were confined to one section of the complementation map of the ad-2 locus.     

Specific reduction of carboxyl groups in peptides and proteins by diborane

1. The reaction of several peptides and proteins with diborane was studied under different conditions to determine those most suitable for the specific reduction of carboxyl groups. 2. In the reaction of model peptides and the cyclic peptides bacitracin and tyrocidin, reduction at 0 degrees was entirely specific for the carboxyl groups without affecting the peptide bonds. Acid amide residues were not reduced. Some tripeptides showed anomalous results in that the C-terminal residue was quite resistant to reduction. 3. Specific reduction of carboxyl groups was achieved in each of the following proteins: human serum albumin, egg albumin, adult human haemoglobin, sperm-whale apomyoglobin, horse heart cytochrome c and egg-white lysozyme. The C-terminal amino acid was usually reduced. 4. Conditions for specific reduction of all available carboxyl groups are not easily found and may vary from one substance to another. Specific reduction of a limited number of available carboxyl groups may be generally accomplished by reactions at -10 degrees . 5. It is suggested that this chemical modification, which has the advantage of permanence, may be useful in studying the role of carboxyl groups in the conformation of proteins and in the biological properties of peptides and proteins.     

A Retraining Program for Inactive Physicians

During the past two years a pilot project was conducted in which 19 inactive physicians were retrained in preparation for resumption of active practice. The initial program consisted of a flexible training program of six months to one year patterned after conventional internship-residency concepts. During the second year the program was modified by providing an initial condensed indoctrination period of two months'' duration especially designed for this purpose, followed by a preceptorship type of training.The project was considered successful in permitting trainees to enter some form of active medical work, or to enroll in formal specialty training. The observations made by the faculty of the program and its accomplishments are discussed in the light of the effort expended and the cost of the project.     

Biochemical Studies of Bacterial Sporulation and Germination XIII. Adenylate Kinase of Vegetative Cells and Spores of Bacillus subtilis

The spore and vegetative cell adenylate kinases of Bacillus subtilis, purified about 1,000-fold, proved indistinguishable by several physical and functional tests, including polyacrylamide gel electrophoresis, DEAE cellulose chromatography, and specificity toward substrates. Adenylate kinase activity in cell extracts, followed throughout growth and sporulation, was found to reach a maximum near the end of exponential growth, remain at that level during sporulation, until shortly before the appearance of refractile forms, and then decline, along with total protein, during the subsequent maturation of the spores. The enzyme, stable in extracts of exponential growing cells, was unstable in extracts of sporulating cells, presumably as a result of degradation by protease(s) appearing after the end of exponential growth.     

Biochemical Studies of Bacterial Sporulation and Germination XIV. Phospholipids in Bacillus megaterium

The principal phospholipids of Bacillus megaterium throughout the cycle of growth and sporulation were found to be phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, and a hitherto unidentified isomer of glycosaminyl-phosphatidylglycerol. Phosphatidylglycerol predominated during vegetative cell growth and then declined as spores developed, whereas diphosphatidylglycerol became more prominent during spore maturation. The latter phosphatide was relatively inaccessible in the vegetative cell and was more accessible in the spore, as judged by solvent extraction under various conditions.     

The Stochastic Theory of Cell Proliferation

A stochastic theory of cell kinetics has been developed based on a realistic model of cell proliferation. A characteristic transit time, _i, has been assigned to each of the four states (G₁, S, G₂, M) of the cell cycle. The actual transit time, t_i, for any cell is represented by a distribution around _i with a variance σ_i². Analytic and computer formulations have been used to describe the time development of such characteristics as age distribution, labeling experiments, and response to perturbations of the system by, for example, irradiation and temperature. The decay of synchrony is analyzed in detail and is shown to proceed as a damped wave. From the first few peaks of the synchrony decay one can obtain the distribution function for the cell cycle time. The later peaks decay exponentially with a characteristic decay constant, λ, which depends only on the average cell-cycle time, , and the associated variance. It is shown that the system, upon any sudden disturbance, approaches new “equilibrium” proliferation characteristics via damped periodic transients, the damping being characterized by λ. Thus, the response time of the system, /λ, is as basic a parameter of the system as the cell-cycle time.     

Spectral Studies of Iron Coordination in Hemeprotein Complexes: Difference Spectroscopy below 250 mμ

In order to evaluate the feasibility of observing the spectral behavior of protein groups in the coordination sphere of the iron in hemeproteins, criteria are developed to determine whether or not the application of difference absorption spectroscopy to the study of complex formation will be successful. Absolute absorption spectra, 300-1100 mmu, from bacterial catalase complexes are displayed, and the infrared bands correlated with magnetic susceptibility values of similar complexes of other hemeproteins. Dissociation constants for the formation of cyanide and azide complexes of metmyoglobin, methemoglobin, bacterial catalase, and horseradish peroxidase are given. Difference spectra, 210-280 mmu, are displayed for cyanide and azide complexes of these hemeproteins. A band at 235-241 mmu is found in the difference spectra of all low-spin vs. high-spin complexes. The factors which favor the assignment of this band to a transition involving a histidine residue are presented.     

The Effect of 2,3,6-Trichlorophenylacetic and 2,2-Dichloropropionic Acids on Nitrite Oxidation

The effects of two herbicides, 2,3,6-trichlorophenylacetic acid, sodium salt, and 2,2-dichloropropionic acid, sodium salt, on nitrite-oxidizing bacteria were studied by the soil perfusion technique. The time of application of 2,3,6-trichlorophenylacetic acid affected its toxicity to the nitrifier. When it was present in the environment as the nitrifier started growth, it was more toxic than if the organisms were allowed to nitrify actively before they were subjected to the herbicide.

The herbicide 2,2-dichloropropionic acid at rates up to 700 ppm had little effect on nitrite oxidation. The toxicity of 2,3,6-trichlorophenylacetic acid for Nitrobacter was reduced by 2,2-dichloropropionic acid irrespective of whether the cells came into contact with the agents before or during active oxidation. The mode of action for this phenomenon has not been determined.