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Publications - Cell and Metabolic Biology
Publications
Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Highly acidic macromolecules are postulated intermediates in tissue mineralization, because they sequester many calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. A prerequisite for biomineralization is the ability of cations like calcium to bind to proteins and to result in concert with appropriate anions like phosphates or carbonates in composite materials with bone‐like properties. For this mineralization process the proteins have to be modified with respect to acidification. In this study we modified the protein collagen by carboxymethylation using glucuronic acid. Our experiments showed unambigously, that Nε‐carboxymethyllysine is the major product of the in vitro nonenzymatic glycation reaction between glucuronic acid and collagen. We hypothesized that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions so that a critical nucleus of ions can be formed, leading to the formation of the mineral. Thus, the self‐organization of HAP nanocrystals on and within collagen fibrils was intensified by carboxymethylation.
Publications
The pigments of Opuntia ficus‐indica fruits, which are derived from the betalain rather than anthocyanin pathway, have an extraordinary range in colour from lime green, orange, red to purple. This is a result from varying concentrations and proportions of about half a dozen betaxanthins and betacyanins. The yellow‐orange betaxanthins are derived from spontaneous condensation of betalamic acid with amines or amino acids. The reddish‐purple betacyanins are enzymatically formed from betalamic acid and cyclo ‐dihydroxyphenylalanine (DOPA) yielding betanidin and further glycosylated on either of the two hydroxyls of the cyclo ‐DOPA moiety. In the present work, degenerated primers were used to obtain partial genomic sequences of two major genes in the biosynthetic pathway for betalains, that is the 4,5‐extradiol dioxygenase which forms the betalamic acid responsible for the yellow colour and a putative 5‐O ‐glucosyltransferase which glycosylates betanidin in Dorotheanthus bellidiformis and may be responsible for the red colour. Differences in the genomic DNA between coloured versus non‐coloured varieties were not found. Regulatory mechanisms seem to independently control pigmentation of O. ficus‐indica fruit tissues for inner core, peel and epidermis. Core pigmentation occurs first and well before fruit maturity and peel pigmentation. Peel pigmentation is fully developed at maturity, presumably related to maximum soluble solids. Epidermal pigmentation appears to be independent of core and peel pigmentation, perhaps because of light stimulation. Similar control mechanisms exist through transcription factors for the major enzyme regulating anthocyanin production in grapes.
This page was last modified on 27 Jan 2025 .
