A physico-chemical study on the polysaccharide ulvan from hot water extraction of the macroalga Ulva.

Results of a study on the solution behaviour of the cell-wall polysaccharide named ulvan obtained from hot water extraction of a flour of Ulva 'rigida' are reported. In particular the spectroscopic properties and ion binding capacity of this charged polysaccharide were studied by circular dichroism and isothermal microcalorimetric titrations in order to gain information on the potential exploitation of this low cost biomass. A marked tendency of this polysaccharide to uptake water was evidenced by studying the proton spin-lattice relaxation times of the solvent, T1, embedded in this highly charged polysaccharide.

A kinetic thermodynamic phenomenological approach to genetic expression of heat-shock proteins.

The approach of viewing complex biochemical phenomena as autocatalytic relaxation processes has been introduced previously (Liquori & Tripiciano, 1980; Liquori & Florio, 1985). In the present work this formalism is extended from its original framework regarding cell growth, to the problem of genetic expression. The case of the heat-shock response in organisms ranging from man to bacteria is discussed. Finally, we give some biochemical examples in which the new approach underlines evident temporal co-operativity.

Quasi-periodic primary structures of core proteins of human T-lymphotropic leukemia retroviruses.

Fourier analysis, previously introduced by Liquori et al. (1983, 1986), has been applied to the primary structures of two core proteins of human T-lymphotropic leukemia retroviruses HTLV-I and HTLV-II. The resulting autocorrelation functions display striking patterns that can be interpreted in terms of an approximately fourfold quasi-periodicity of the primary structures. Self-alignments of the amino acid sequences containing a few gaps are consistent with the above finding and suggest that the tertiary structure of these two homologous core proteins contains alpha-helical and delta-helical segments, the latter being characteristic of the threefold helix present in collagen structure.

Pattern recognition of sequence similarities in globular proteins by Fourier analysis: a novel approach to molecular evolution.

A new algorithm is introduced for analyzing gene-duplication-independent (orthologous) and gene-duplication-dependent amino acid sequence similarities between proteins of different species. It is based on the calculation of an autocorrelation function D(x) as a Fourier series analogous to that used in crystal analysis by x-ray diffraction. The primary structure of the protein is decomposed into "homopolypeptide-defective sequences" containing identical or similar amino acid residues and vacancies corresponding to the missing amino acid residues. The Fourier transforms F(h) simulating the diffraction patterns of defective linear gratings corresponding to the defective homopolypeptide sequences are calculated. The squared F(h) values are then used as coefficients of Fourier series corresponding to the autocorrelation functions D(x). A peak of D(x) corresponds to a vector of length x, which is the distance between two identical amino acid residues. It is pointed out that optical diffraction methods, instead of computer methods, would also be useful. It is shown through a number of examples that this method allows satisfactory pattern recognition of homologies and internal duplications of an initial segment of the polypeptide chain. In the latter case the value of the above method may be seen from the fact that it detects repeated duplications in proteins such as spinach ferredoxin and myoglobin, for which other methods had either failed or given inconclusive results. The above approach appears most promising for studies of molecular evolution and structure-sequence correlations.

A thermodynamic study of sperm-egg interaction.

We have studied the binding of spermatozoa to the receptor sites on the vitelline coat (VC) of glycerol-treated eggs (ghost eggs) of the Ascidian, Ciona intestinalis (Protochordate). Glycerol treatment cytolyses the egg without affecting the ability of the VC to bind spermatozoa in a species-specific manner; however, in this system binding is not followed by the acrosome reaction. The ghost eggs are metabolically inert. As a base line for our analysis, we have studied the concentration-dependent heat evolved and oxygen consumption of spermatozoa when diluted in sea water. The process has been analyzed on the basis of equations derived by Liquori and Tripiciano to describe cell growth. Upon binding to the ghost eggs, the spermatozoa produce an explosive heat evolution (excess heat) which is not accompanied by oxygen consumption. The excess heat produced plotted against sperm concentration (at constant egg concentrations) gives an asymmetric bell-shaped curve. This is interpreted as being due to the competitive effect of sperm agglutination at a high sperm concentration. It is concluded that only spermatozoa that attach singly (monomeric spermatozoa) to the egg undergo metabolic activation.

A theoretical equation for diauxic growth and its application to the kinetics of the early development of the sea urchin embryo.

The equation for diauxic growth is derived as a linear combination of two functions describing a slow and a fast rate of cell multiplication. The growth curve displays the typical biphasic shape, containing two sigmoidal branches. The curve fits very satisfactorily experimental data describing the increase of cell number in developing sea urchin embryos as a function of time, thus suggesting the presence of diauxia in this system. The hypothesis is formulated that diauxia in sea urchin embryos is the expression of two distinct metabolic pathways that result in a slow and a fast division process.