Effect of Urea on the Cold Precipitation of Protein in the Lens of the Dogfish

Metabolic Studies on the Cold Precipitable Protein of the Lens*

“…(Whitney, P. L. 8s Tanford, C. 1962). The hypothesis that gamma crystallin behaves as a cryoprotein because of exposed hydrophobic groups, is consistent with the observation that low concentrations of urea (0.3 M) are capable of preventing this phenomenon (Zigman, S. 8s Lerman, S. 1965b). It is possible that alpha and/or beta crystallin (when present in a concentration above that of gamma crystallin) prevents the cold precipitation reaction by means of hydrophobic bonding with gamma crystallin thereby reducing the number of exposed hydrophobic groups and increasing the solubility of such a protein complex.…”

“…The apparent sudden fall in the level of gamma crystallin in the galactose cataract may be due to a precipitation of a considerable amount of previously soluble gamma crystallin. Previous experiments have noted a significant decrease in the concentration of total soluble lens proteins in rats maintained on a galactose diet (Dische, Z. et a1 1956;Lerman, S. 1960).…”

A current perspective on the compensatory effects of urea and methylamine on protein stability and function

“…Urea, although a waste product is also accumulated in the mammalian kidney at very high concentrations (up to 3-4 M) and contributes in osmo-adaptation (Yancey, 1988;Yancey, 1994;Yancey, 2001;Yancey et al, 1982). For the survival of these animals under such large concentration of urea, three adaptational hypothesis have been suggested which include the urea insensitiveness of some proteins; for instance, actomyosin ATPases of elasmobranchs and IgNAR (Ig new antigen receptor) antibodies of sharks are more stable in urea (Bonaventura et al, 1974;Feige et al, 2014;Hasnain and Yasui, 1986;Yancey, 1985); urea requirement by some proteins, for instance, in case of lactate dehydrogenase and eye lens protein of elasmobranches wherein urea was found to maintain optimum K m for pyruvate and prevented the precipitation of the latter at low temperatures (Yancey and Somero, 1978;Zigman et al, 1965); and urea-counteracting osmolyte system; for instance, the activity of an enzyme in the presence of urea is maintained by the co-accumulation of another stabilizing osmolyte (Yancey, 1988;Yancey et al, 1982;Yancey and Somero, 1979;Yancey and Somero, 1980). Among these three, the last one seems to be the primary one.…”

Myosin light chain of shark fast skeletal muscle exhibits intrinsic urea-resistibility

“…Marine elasmobranch fish swim like teleosts with small amounts of urea in their body, indicating that proteins within their body can tolerate urea. The lens protein of dogfish Mustelus canis does not precipitate under 10 °C in the presence of urea but does in the absence of urea 9 . The oxygen affinity of clearnose skate Raja eglanteria hemoglobin is maintained up to 5 M urea 10 .…”