Fractal nature in fat crystal networks

The determination of the mechanical and rheological characteristics of several plastic fats requires a detailed understanding of the microstructure of the fat crystal network aggregates. The fractal approach is useful for the characterization of this microstructure. This review begins with information on fractality and statistical self-similar structure. Estimations for fractal dimension by means of equations relating the volume fraction of solid fat to shear elastic modulus G’ in linear region are described. The influence of interesterification on fractal dimension decrease (from 2,46 to 2,15) for butterfat-canola oil blends is notable. This influence is not significant for fat blends without butterfat. The need for an increase in research concerning the relationship between fractality and rheology in plastic fats is emphasized.La determinación de las características mecánicas y reológicas de ciertas grasas plásticas requiere conocimientos detallados sobre las microestructuras de los agregados que forman la red de cristales grasos. El estudio de la naturaleza fractal de estas microestructuras resulta útil para su carac­terización. Este artículo de información se inicia con descripciones de la dimensión fractal y de la "autosimilitud estadística". A continuación se describe el cálculo de la dimensión fractal mediante ecuaciones que relacionan la fracción en volumen de grasa sólida con el módulo de recuperación (G') dentro de un comportamiento viscoelástico lineal. Se destaca la influencia que la interesterificación ejerce sobre la dimensión fractal de una mezcla de grasa láctea y aceite de canola (que pasa de 2,64 a 2,15). Esta influencia no se presenta en mezclas sin grasa láctea. Se insiste sobre la necesidad de incrementar las investi­gaciones sobre la relación entre reología y estructura fractal en grasas plásticas.Peer reviewe

Die Kultur der Kulturlosen, uin Blick in die Anfange menschlicher Geistesbetatigung. Zwolfte Auflage.

Kosmos, Gesellscuaft der Naturfreunde.LEIDSSTELSELOPLADEN-RUG0

Primary sequence of the EcoRII endonuclease and properties of its fusions with beta-galactosidase

The EcoRII endonuclease cleaves DNA containing the sequence CC(A/T)GG before the first cytosine. The methylation of the second cytosine in the sequence by either the EcoRII methylase or Dcm, a chromosomally coded protein in Escherichia coli, inhibits the cleavage. The gene for the EcoRII endonuclease was mapped by analysis of derivatives containing linker insertions, transposon insertions, and restriction fragment deletions. Surprisingly, plasmids carrying the wild-type endonuclease gene and the EcoRII methylase gene interrupted by transposon insertions appeared to be lethal to dcm+ strains of E. coli. We conclude that not all the EcoRII/Dcm recognition sites in the cellular DNA are methylated in dcm+ strains. The DNA sequence of a 1650-base pair fragment containing the endonuclease gene was determined. It revealed an open reading frame that could code for a 45.6-kDa protein. This predicted size is consistent with the known size of the endonuclease monomer (44 kDa). The endonuclease and methylase genes appear to be transcribed convergently from separate promoters. The reading frame of the endonuclease gene was confirmed at three points by generating random protein fusions between the endonuclease and beta-galactosidase, followed by an analysis of the sequence at the junctions. One of these fusions is missing 18 COOH-terminal amino acids of the endonuclease but still displays significant ability to restrict incoming phage in addition to beta-galactosidase activity. No striking similarity between the sequence of the endonuclease and any other protein in the PIR data base was found. The knowledge of the primary sequence of the endonuclease and the availability of the various constructs involving its gene should be helpful in the study of the interaction of the enzyme with its substrate DNA

Cloning and characterization of the HpaII methylase gene.

The HpaII restriction-modification system from Haemophilus parainfluenzae recognizes the DNA sequence CCGG. The gene for the HpaII methylase has been cloned into E. coli and its nucleotide sequence has been determined. The DNA of the clones is fully protected against cleavage by the HpaII restriction enzyme in vitro, indicating that the methylase gene is active in E. coli. The clones were isolated in an McrA-strain of E. coli; attempts to isolate them in an McrA+ strain were unsuccessful. The clones do not express detectable HpaII restriction endonuclease activity, suggesting that either the endonuclease gene is not expressed well in E. coli, or that it is not present in its entirety in any of the clones that we have isolated. The derived amino acid sequence of the HpaII methylase shows overall similarity to other cytosine methylases. It bears a particularly close resemblance to the sequences of the HhaI, BsuFI and MspI methylases. When compared with three other methylases that recognize CCGG, the variable region of the HpaII methylase, which is believed to be responsible for sequence specific recognition, shows some similarity to the corresponding regions of the BsuFI and MspI methylases, but is rather dissimilar to that of the SPR methylase