The hydrolysis by thermolysin of dipeptide derivatives that contain substituted cysteine

1. The preparation of protected dipeptides of the form acetylglycylamino acid amides is described, where the amino acid is phenylalanine, leucine, valine, alanine, S-methylcysteine, S-ethylcysteine, S-benzylcysteine and S-phenylcysteine. 2. Kinetic parameters for the thermolytic hydrolysis of these blocked dipeptides are reported. The rate of hydrolysis was fastest when the amino acid was leucine or phenylalanine, slower when it was S-methylcysteine, valine or S-ethylcysteine, much slower when it was alanine, and negligible for S-phenylcysteine or S-benzylcysteine. 3. The results are compared with those for similar dipeptide derivatives with benzyloxycarbonyl and furylacryloyl blocking groups, which are hydrolysed faster.     

Organic acid production during methylotrophic growth of Eubacterium limosum B2: displacement towards increased butyric acid yields by supplementing with acetate

Summary During anaerobic growth on methanol/CO₂ the fermentative bacterium Eubacterium limosum B2 produced mixtures of acetic and butyric acids as overflow metabolites. The proportion of each product was shown to vary according to the initial acetate concentration. At low concentrations, acetate provoked a displacement of the organic acid ratio culminating in homobutyric fermentations at 100 mM initial acetate. This metabolic shift was accompanied by a proportionate increase in the methanol dissimilated to CO₂, enabling a constant NAD(P)H₂/NAD(P) metabolite pool to be maintained. Higher initial acetate concentrations could not be balanced by further changes to the substrate stoichiometry and resulted in less rapid growth. The yield of butyric acid was enhanced further by some consumption of acetate. A mathematical model is presented relating initial acetate concentration to butyric acid production.     

Effects of various organic acid supplements on growth rates of Eubacterium limosum B2 on methanol

Summary During anaerobic growth on methanol, Eubacterium limosum B2 produces acetic and butyric acids as overflow metabolites, but can be induced to produce other organic acids. All organic acids (C₂–C₆) tested had a similar effect on growth, although the toxicity of each was different e.g. increasing inhibition by acids of increasing chain length. Inhibition was only observed above a threshold concentration related to the molecular size of the organic acids. At higher concentrations the degree of inhibition was a linear function of concentration. In a mathematical treatment of the data the inhibition constant (K _p) was shown to be proportionate to the threshold value (P _c) of each organic acid and accurately predicted the growth characteristics of Eubacterium limosum on methanol following the addition of organic acid supplements.     

Preliminary X-ray crystallographic study of the turkey lens protein, δ-crystallin

The structural protein, δ-crystallin, has been purified and crystallized from adult turkey lens. The crystals are orthorhombic and normally belong to space group P2₁2₁2 with unit cell dimensions $\text{a = 99.9(2)}\text{A}\text{?}\text{, b = 133.4(3)}\text{A}\text{?}\text{and}\text{c = 69.1(2)}\text{A}\text{?}$. This corresponds to two molecules of molecular weight approximately 200,000 per unit cell. A second crystal form has also been found in which b and c increase to 135.4(3) Å and 140.0(3) Å. respectively, indicating four molecules per unit cell.     

The effects of inhibitors of RNA and protein synthesis on cytological development during meiosis

Summary An examination of the correlation between RNA and protein synthesis occurring during meiosis and cytological development was made in Trillium erectum microsporocytes. Various reagents known to act at various steps of protein biosynthesis were administered to cultured buds at different developmental stages with more or less effect depending on the stage rather than the reagent.Syntheses were found to be necessary for continued development of the microsporocytes during early prophase. Synthesis during meiotic prophase was also necessary for the maintainance of the condensed state of the late prophase chromosomes, the initial separation of the paired homologous chromosomes, and the orderly function of the spindle. Cytokinesis was readily disturbed at all treatment times. Pairing of homologous chromosomes was not affected and the prespecification of pairing is believed to occur at or near the time of DNA synthesis.The results indicate that the syntheses occurring during meiosis can be correlated with cytological developmental processes.Based on a thesis presented in partial fulfillment of the requirements for the Ph. D. degree at the University of Illinois, Department of Botany.     

Phenomenological description of active transport of salt and water

The phenomenological definition of active transport by Kedem and the methods of Kedem and Katchalsky have been used to obtain practical equations describing active transport in the single salt and bi-ionic systems. Procedures were devised to evaluate the required set of 10 coefficients for the single salt case and 15 for the bi-ionic. Three of these coefficients are unusual. They express the effects of active transport, i.e. of entrainment between metabolism and the conventional transport flows: active salt transport coefficient, a volume pump coefficient, and an electrogenicity coefficient. In the bi-ionic case a new passive coefficient, lambda, was used to express the linkage between the fluxes of the two salts. However, if primary active transport involves only one ion, for example in the bi-ionic case, 12 coefficients suffice and certain relations can be predicted between the practical coefficients. Particular types of primary active transport could be identified by this means. The relation of active transport to membrane electrogenesis was also examined and the flux ratio equation was rederived in terms of the practical coefficients. Applications to specific parallel and series membrane systems have been analyzed.     

Analysis of life tables with grouping and withdrawals.

A number of individuals is observed at the beginning of a period. At the end of the period the number is surviving, the number who have died and the number who have withdrawn are noted. From these three numbers it is required to estimate the death rate for the period. All relevant quantities are supposed independent and identically distributed for the individuals. The likelihood is calculated and found to depend on two parameters, other than the death rate, and to be unidenttifiable so that no consistent estimators exist. For large numbers, the posterior distribution of the death rate is approximated by a normal distribution whose mean is the root of a quadratic equation and whose variance is the sum of two terms; the first is proportional to the reciprocal of the number of individuals, as usually happens with a consistent estimator; the second does not tend to zero and depends on initial opinions about one of the nuisance parameters. The paper is a simple exercise in the routine use of coherent, Bayesian methodology. Numerical calucations illustrate the results.     

Factors affecting population development within seawater-displaced fuel tanks

Abstract Populations within model seawater-displaced fuel tanks developed as a succession of eukaryotic species. Growth of filamentous fungi was preceded by the growth of several yeast species. More rapid initiation of growth by filamentous fungi was associated with extracellular metabolites produced by yeasts: both the pH flux towards more acidic conditions and the spore germination induction effect influenced population development. The relative binding affinity of each species for the insoluble hydrocarbon fuel is proposed as a major characteristic determining which species proliferated at the fuel-water interface.     

Degradation of α-Ketoglutarate by Veillonella alcalescens

Veillonella alcalescens degrades alpha-ketoglutarate to CO(2), H(2), and propionate by a thioclastic mechanism.