The surface tension of aqueous solutions of ? : ?-dihydroxy-?-aryloxypropanes

1. The double-isotope concept [Arias, Doyle & Schimke (1969) J. Biol. Chem. 244, 3303--3315] for the measurement of protein turnover was used to estimate the turnover rates of protein subunits from rat liver submitochondrial fractions resolved by means of polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. NaH14CO3 and [5-3H]arginine were used as first and second precursors respectively. 2. Marked heterogeneity of protein subunit turnover rates is seen for protein subunits from water-soluble, salt-soluble and Tween 20-soluble mitochondrial proteins. 3. Much lower heterogeneity is seen in the turnover of protein subunits in Triton X-100-soluble material not binding to DEAE-cellulose at low ionic strength. The relative rates of turnover of proteins in this fraction are lower than for proteins in any other submitochondrial fraction. This fraction contains the integral membrane proteins. 4. Incorporation of [3H]arginine into subunits of the cytochrome oxidase complex is greatest for subunits with molecular weights in excess of 20000. 5. No correlation is seen between protein subunit size and the rate of turnover of the protein subunits in any of the submitochondrial fractions.

Section: Discussionmentioning

confidence: 38%

Relative rates of turnover of subunits of mitochondrial proteins

Walker¹,

Burgess²,

Mayer³

1978

“…An alternative explanation is that the rapid labelling could be a result of a specific induction of the lysosomal system by Triton WR-1339 treatment. It has been reported that Triton WR-1339 leads to an induction of cathepsins B and D in rat liver (Dean, 1975). We have found that ATPase activity also increases after Triton WR-1339 treatment (Table 3); however, N-acetyl-fl-D-glucosaminidase activity did not increase.…”

Section: Discussionmentioning

confidence: 54%

Characterization of the membrane proteins of rat liver lysosomes. Composition, enzyme activities and turnover

Burnside¹,

Schneider²

1982

Lysosomes prepared from the livers of untreated rats and from the livers of rats injected with either Triton WR-1339 or dextran yielded membranes that were similar in both polypeptide composition and activities of ATPase and acid 5'-nucleotidase. The administration of Triton WR-1339 (and dextran) resulted in an increase in ATPase activity of liver homogenates that was associated with a parallel increase in the ATPase activity of the lysosomal membrane. On the other hand, plasma membranes appear to be different from lysosomal membranes with respect to polypeptide composition and enzyme activities. The ATPase activity of lysosomal membranes is not affected by ouabain and suramin, inhibitors of the plasma-membrane ATPase. The plasma-membrane alkaline 5'-nucleotidase has little activity at acid pH. Pulse-labelling of lysosomal membranes with [3H]fucose and with [3H]- and [14C]-leucine occurred rapidly, faster than labelling of plasma membranes. The labelling kinetics indicate that lysosomal membranes may be assembled independently of plasma membranes. These data suggest that, in liver, little bulk transport of plasma membrane to lysosomes takes place, and lysosomal-membrane proteins may not be derived from those of plasma membranes.

“…This description of the turnover of lysosomalmembrane proteins can also accommodate the observation that they do not show a clear correlation between subunit size and half-life (Dean, 1975b;Wang & Touster, 1975), unlike endoplasmic-reticulum-membrane proteins. During digestion in vitro ofsoluble proteins by lysosomal or other proteinases, those of short half-life in vivo (which are enriched in large-subunit proteins) are degraded fastest.…”

mentioning

confidence: 77%

“…In the case of autophagy by lysosomal invagination, cytosol proteins are sequestered (Dean, 1975a), but this process should also result in degradation of lysosomal membrane, apparently as a unit. However, it is clear that lysosomal-membrane proteins have quite heterogeneous half-lives (Dean, 1975b;Wang & Touster, 1975). If invagination and unit degradation accounted for a large part of lysosomal-membrane turnover, this observation would be difficult to explain.…”

mentioning

confidence: 99%

Lysosomes and membrane recycling. A hypothesis

Dean¹

1977

A mechanism for intralysosomal membrane recycling is proposed. After invagination of the lysosomal membrane during autophagy, intralysosomal vesicles are formed. It is suggested that membrane can bleb out from these internal vesicles, probably in the form of very small vesicles, and return to the external lysosomal membrane by membrane fusion. This mechanism would conserve lysosomal membrane during autophay, and is analogous to current models of plasma-membrane recycling. Its relationship to turnover of lysosomal-membrane proteins and other proteins is discussed.