The relationship between elastin and an acidic protein in mammalian uterus.

Abstract

Alkali-purified elastin from uterus was found to be intimately associated with an acidic protein, similar in amino acid composition to protein fractions isolated from other tissues by several workers. Studies on the incorporation of glycine-C14 into both soluble and insoluble forms of the acidic protein in rat uterus in vivo suggest that the acidic protein is easily extractable when newly synthesized and becomes insoluble with time. The most highly aggregated form of the acidic protein is relatively insoluble and thus difficult to separate from elastin. The concentration of dityrosine, an o, o'-biphenol analogue of tyrosine, has been found to correlate with the degree of aggregation in the alkali-soluble protein fractions of embryo chick aorta. The same may be true in uterus, but dityrosine, by itself, cannot account for the progression of acidic protein to its insoluble form. The concentration of an unknown fluorescent compound (A/E:360/:< 415 nm) correlates with decreasing solubility of acidic protein, but its identity, relationship to dityrosine, and significance are unknown. Ion-exchange chromatography of a partial acid hydrolysate of the alkali-insoluble protein from human uterus yielded a protein fragment with amino acid composition intermediate to elastin and the soluble acidic protein. The possibility of a covalent linkage between the two protein species thus cannot be discounted. In rat uterus, electron microscopic and biochemical evidence is presented for active fibrogenesis, particularly in pregnancy. The functional significance of the acidic protein is not well understood but uterus contains an unusually high proportion of the protein in both soluble and insoluble forms.