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Biomedical subjects

J F Dice

Publications and source records attributed to J F Dice.

81 records · Page 5Linked to original sources
PubMed1975

Relationship between in vivo degradative rates and isoelectric points of proteins.

Previous studies have shown that in mammalian cells proteins of large molecular weight are degraded more rapidly than small ones. Evidence is presented here that half-lives of proteins are also related to their isoelectric points. A double-isotope method was used to compare degradative rates of soluble proteins separated by isoelectric focusing. In rat liver, skeletal muscle, kidney, and brain, more rapid rates of catabolism were found for acidic protein fractions than for neutral or basic ones. Acidic proteins also tended to be degraded faster in several mouse tissues. A literature survey confirmed this trend. For 22 proteins from rat liver, a highly significant correlation was found between rates of degradation and isoelectric points (r = 0.824; P less than 0.01). This relationship between isoelectric point and half-life appears to be distinct from that between protein size and half-life.

Animals↗
PubMedDate not supplied

Cellular theories of aging as related to the liver.

The age-associated decline in function of several organs, including the liver, may be caused by mechanisms operating on the cellular level. Fibroblasts and several other cell types derived from normal individuals have limited lifespans in culture, and several abnormalities described for senescent cultured fibroblasts also apply to hepatocytes and other cell types obtained from aged organisms. Cellular theories of aging can be divided into two broad and overlapping categories: (a) those that view cell death as an actively programmed developmental process, and (b) those that consider cellular aging to result from a passive accumulation of errors in macromolecules. These theories are not necessarily mutually exclusive, and many of the phenotypic changes in senescent hepatocytes, fibroblasts and other cells are compatible with several different theories. The challenge for the future is to distinguish primary causes from secondary consequences of cellular aging so that rational attempts to intervene in the aging process are possible.

Aging↗
PubMedDate not supplied

Ubiquitin pools, ubiquitin mRNA levels, and ubiquitin-mediated proteolysis in aging human fibroblasts.

Senescent cells have less free ubiquitin and more ubiquitin-protein conjugates than do young cells. The ubiquitin-protein conjugates are heterogeneous in size but contain prominent bands at 106, 55, and 22 kDa. The age-related increase in ubiquitin-protein conjugates applies primarily to the 55-kDa band, while the 106-kDa and 22-kDa conjugates change little with age. Ubiquitin mRNA levels do not change with age, and the ability of cells to degrade two proteins that are good substrates for ubiquitin-mediated proteolysis is unaltered by aging. These results indicate that an increase in ubiquitin-protein conjugates does not necessarily reflect alterations in ubiquitin-mediated proteolysis. Furthermore, an overactive pathway of ubiquitin-mediated proteolysis does not appear to contribute to the proliferative arrest in senescent cells.

Actins↗