Dolichol alters GABA uptake and high affinity binding of agonist to rat brain synaptic plasma membranes

Age-related changes in the autophagic proteolysis of rat isolated liver cells: effects of antiaging dietary restrictions

Autophagy is a process that sequesters and degrades organelles and macromolecular constituents of cytoplasm for cellular restructuring and repair and as a source of nutrients for metabolic use in early starvation. The effects of two antiaging dietary regimens (initiated in rats at the age of 2 months), namely, 40% dietary restriction (DR) and every-other-day ad-libitum feeding, that exhibited different effects on metabolism and similar effects on longevity on the age-related changes in the regulation of autophagic proteolysis were studied by monitoring the rate of valine release in the incubation medium from isolated liver cells of male albino Sprague-Dawley rats aged 2, 6, 12, 18, 24, and 27 months. (The liver cells were incubated in vitro with added amino acids and 10(-7) M insulin or glucagon.) Age-matched male albino Sprague-Dawley rats fed ad libitum served as a control. Results show that in ad-libitum-fed rats, after a transient increase by age 6 months, autophagic proteolysis and regulation by amino acid exhibit a dramatic age-related decline, and that the age-related changes are prevented by dietary antiaging intervention. A comparison shows that the protective effects of DR and every-other-day ad-libitum feeding are partially different in 24-month-old rats (but the beneficial effects of the two diets on regulation of autophagic proteolysis are always similar). With regard to endocrine regulation, results confirm that the liver cell response to glucagon (but not to insulin) declines with increasing age, and they show that antiaging DRs significantly improve the effects of glucagon (and have no effect on the response to insulin). The interactions of age by diet, glucagon (and in older rats, insulin), and amino acids are significant. It is concluded that DR significantly improves the susceptibility of liver cells to lysosomal degradation, and it prevents decline with increasing age. It is suggested that improved liver autophagy and lysosomal degradation might be part of the antiaging mechanisms of DR.

Characterization and localization of a long-chain isoprenyltransferase activity in porcine brain: proposed role in the biosynthesis of dolichyl phosphate

Pig brain microsomes catalyzed the enzymatic transfer of radiolabeled isoprenyl groups from [1-14C]isopentenyl pyrophosphate [( 1-14C]I-P-P) into long-chain polyisoprenyl pyrophosphates (Poly-P-P) and unidentified neutral lipids. The brain isoprenyltransferase activity synthesizing the Poly-P-P (1) required 5 mM Mg2+ and 10 mM vanadate ions for maximal activity; (2) exhibited an apparent Km of 8 microM for I-P-P; (3) utilized exogenous farnesyl pyrophosphate and two stereoisomers of geranylgeranyl pyrophosphate as substrates; (4) was optimal at pH 8.5; and (5) was stimulated by dithiothreitol. The major products were identified as C90 and C95 allylic Poly-P-P on the basis of the following chemical and chromatographic properties: (1) the intact product co-chromatographed with authentic Poly-P-P on silica-gel-impregnated paper; (2) the major product was converted to a compound chromatographically identical to polyisoprenyl monophosphate (Poly-P) by alkaline hydrolysis; (3) treatment of the labeled Poly-P with wheat germ acid phosphatase or mild acid yielded neutral labeled products; (4) the KOH hydrolyzed product coeluted with authentic Poly-P from lipophilic Sephadex LH-20; and (5) the labeled lipids produced by enzymatic dephosphorylation had mobilities identical to fully unsaturated polyisoprenols containing 18 (C90) and 19 (C95) isoprene units when analyzed by reverse-phase chromatography. When subcellular fractions from rat brain gray matter were compared, the highest specific activity was found in the heavy microsomes. These results demonstrate that brain contains an isoprenyltransferase activity, associated with the rough endoplasmic reticulum, capable of synthesizing long-chain Poly-P-P. The enzymatic reactions by which the Poly-P-P intermediate is converted to dolichyl phosphate remain to be elucidated.