The troublesome crosslinks of elastin

Photolysis and ozonolysis of desmosine and elastolytic peptides

This paper describes the combined effects of photolysis and ozonolysis upon the main interchain crosslinks of elastin, desmosine and isodesmosine. Photolysis of purified (iso)desmosines in solution leads to the cleavage of the pyridinium rings to give lysine and an analogue of glutaconic aldehyde which is deformylated to a stable compound absorbing at 242 nm. This photoproduct is subsequently fragmented by ozone into glutamic, alpha-aminoadipic and possibly alpha-amino-delta-oxocaproic acids. However the yields of these different compounds are very low because we observed that numerous competing side reactions (polymerisation, recyclisation) accompany the photoozonolytic decomposition of the pyridinium rings of free (iso)desmosines. The results are clearer when reticulated elastolytic peptides are photoozonolysed. The (iso)desmosines, covalently linked in these peptides, are cleaved into lysine, glutamic and alpha-aminoadipic acids (in a ratio 2:1) with yields corresponding to 80-90% of those expected from the decomposition of the (iso)desmosines originally present in the peptide fraction. We have also observed that ozonolysis alone degraded another crosslink present in these peptides, the aldol condensation product, resulting in the production again of glutamic and alpha-aminoadipic acids in amounts consistent with the known concentrations of this particular crosslink in elastin. Finally we noted that the complete photoozonolytic degradation of the (iso)desmosines present in a semi purified reticulated elastolytic fraction resulted in a shift of the size distribution of these peptides toward lower values. It is not certain however that this shift, indicative of a freeing of the polypeptide chains from their original three dimensional network, is due uniquely to the cleavage of the (iso)desmosines. Indeed we have observed that tyrosine and phenylalanine were also degraded during photoozonolysis. Not knowing the mechanism of this degradation it is impossible to rule out the possibility that concomitant cleavages of peptide bonds did occur.

Cross-link formation at the head-tail junction of mammalian spermatozoa during aging is dependent on sperm motility

A high percentage of the heads of mouse, hamster, and rabbit spermatozoa were detached from their tails by vortexing a suspension of spermatozoa that had been incubated with dithiothreitol (DTT), a sulfhydryl reagent. Similar treatment of spermatozoa that had been aged under physiologic conditions for several hours and were still motile before reaction with DDT gave a much lower percentage of head detachment. This stabilization of the sperm head-tail junction developed only if spermatozoa were motile during aging. n-Butylamine also induced head detachment of mouse spermatozoa. Motile and immotile mouse spermatozoa became resistant to n-butylamine when aged in physiologic medium and buffer, respectively. However, stabilization developed much faster if spermatozoa were motile. Stabilization of the head-tail junction of motile spermatozoa to the reagents occurred over the time periods required for capacitation and the development of hyperactivated motility. Development of resistance to the two reagents may be biochemical events associated with capacitation.

Breakdown of Diazotized Proteins and Synthetic Substrates by Rumen Bacterial Proteases

Several different kinds of substrate were used to investigate the proteolytic activity of rumen bacteria and of proteases released from rumen bacteria by blending (“coat proteases”). These substrates included diazotized feed proteins and diazotized soluble and insoluble pure proteins. It was concluded that, while solubility was an important factor, the secondary and tertiary structure of a protein had a major influence on its rate of digestion. The resistance of elastin congo red to digestion indicated that similar fibrous proteins in plant material might resist proteolytic attack by rumen bacteria. Coat proteases had a broad specificity, including several exo- and endopeptidase activities, as determined by using synthetic peptide substrates.

Microbial ecology and activities in the rumen: part 1

This review describes the progress which has been made during the last 10 to 15 years in the field of rumen microbiology. It is basically an account of new discoveries in the bacteriology, protozoology, biochemistry, and ecology of the rumen microbial population. As such it covers a wide range of subjects including the isolation and properties of methanogenic bacteria, the role of rumen phycomycete fungi, anaerobic energy conservation, and general metabolic aspects of rumen microorganisms. It also attempts, however, to describe and develop new concepts in rumen microbiology. These consist principally of interactions of the microbemicrobe, microbe-food and microbe-host types, and represent the main areas of recent advance in our understanding of the rumen ecosystem. The development of experimental techniques such as chemostat culture and scanning electron microscopy are shown to have been instrumental in progress in these areas. The paper is concluded with an assessment of our present knowledge of the rumen fermentation, based on the degree of success of experiments with gnotobiotic ruminants inoculated with defined flora and in mathematical modeling of the fermentation. The efficacy of chemical manipulation of the fermentation in ruminant is also discussed in this light.