Albert I. Lansing

Synthesis and degradation of liver proteins in young and old rats

Abstract The report describes the study of the in vivo synthesis and degradation of ferritin as an example of an intracellular liver protein, albumin, as an example of a protein secreted by the liver, and total liver protein in young and old rats. In addition, possible age changes in the amounts of these proteins were investigated. Several biochemical changes occur with age. 1. 1. There is twice as much ferritin and about 4 times as much iron in old rat liver ferritin as in livers from young rats. 2. 2. The accumulation of ferritin in old rats appears to be due to a decreased rate of degradation. 3. 3. Albumin synthesis is increased in old rats. 4. 4. Albumin synthesis in young rats can be increased by removing blood from the animals. Old rats do not respond to the removal of blood by increased albumin synthesis. Finally, there is a labeling pattern of ferritin with time which is different from that of total liver protein suggesting two distinct steps, synthesis of subunits and assembly into ferritin molecules. The results suggest that in order to study age-related changes one should consider changes in specific proteins that might be masked if only total proteins are investigated. In addition, certain changes might become apparent only if the system is manipulated, in our case, induction of albumin synthesis by removal of blood from the animal

Synthesis of the plasma membrane of the liver cell

Abstract The steps involved in the synthesis of a plasma (surface) membrane are completely unknown. For the newly-synthesized protein constituents of the membrane, four possibilities have been considered. First, newly-formed proteins are added directly to the membrane; second, they mix with a soluble pool and are then incorporated into the membrane; third, they are assembled into complex units that are then built into the membrance; and fourth, they are incorporated into a precursor membrance that is later converted into a plasma membrane. The work presented here shows that proteins may be formed several hours before they are built into the liver plasma membrane. Thus, a direct incorporation of all new protein can be ruled out. It is not yet possible, however, to distinguish among the remaining three possibilities.

In vitro synthesis of microsomal protein and albumin in young and old rats.

Abstract 1. 1. Protein and serum albumin synthesis was investigated with isolated liver microsomes from young and old rats. Albumin synthesis of old rats, based on mg protein, is 50 % higher than that of young rats, but there is no difference in total protein synthesis. 2. 2. The increased albumin synthetic activity resides in the microsomal particles and not in the cell sap. 3. 3. The albumin synthesis of young rats can be stimulated by bleeding. Increased albumin synthesis reaches its peak at 3 h after bleeding and is 40 % higher than in non-bled young rats, whereas in old rats, bleeding does not further increase albumin synthesis. 4. 4. The cell sap fraction from bled rats, either young or old, has a stimulating effect on albumin synthesis by the microsome fraction from young rats.

Functional regeneration in liver of old rats after partial hepatectomy

Abstract This study suggests that changes in liver protein metabolism occurring with age are not due to changes in the genome. Regenerating rat liver in old animals has regained functional properties of young rat liver. Specifically albumin synthesis, which is elevated in old animals, returns to young rat levels in old rats for several weeks after partial hepatectomy. Both in vivo and in vitro studies support this evidence. Old rat liver ferritin also undergoes changes in regenerating liver. The amount of ferritin iron/g liver falls to one half, the amount of iron/mg ferritin protein drops, but the amount of ferritin protein/g liver remains constant in regenerated old rat liver. The half-life of ferritin in regenerated old rat liver (2·3 days) is much shorter than in old rat liver controls (3·9 days) and approaches that of young rat liver ferritin (2·1 days). Determinations were done at a time when liver weight had been fully restored following removal of 67 per cent of the liver. Functional properties of old rat liver are restored by 12 weeks after partial hepatectomy.

Etiology of increased albumin synthesis in old rats

Abstract We have investigated albumin synthesis and excretion of albumin into the urine in young and old rats. Evidence is provided to suggest that the higher rate of excretion of albumin into the urine in old rats is not responsible for the increased synthesis. Albumin synthesis in young and old animals was determined after partial hepatectomy, injection of serum protein into the tail vein, and after aminonucleoside puromycin induced nephrosis. For several weeks after partial hepatectomy, an operation that should not effect nephrosis in old rats, albumin synthesis in old rats is decreased. Injection of serum does not decrease albumin synthesis but causes an increase in the amount of albumin excreted into the urine. Aminonucleoside puromycin induced nephrosis does not stimulate albumin synthesis to a significant extent. It is concluded that the rate of excretion of albumin into the urine is a function of the albumin levels in the serum and that synthesis of albumin is not regulated to a great extent by the rate of excretion.

Localization of Proelastase in the Goose-Fish (Lophius piscatorius).

Summary A proelastase resembling that of the pig and the rat has been found in the pancreas of the Goose-fish. It is localized in the acinar portion of the pancreas, both in the mesenteric bands and in the capsule of the principal islet. However it is absent from the endocrine portion of this organ.