Retinol esterification by mammary gland microsomes from the lactating rat.
نویسنده
چکیده
Because vitamin A in milk is largely present as esterified retinol while blood plasma predominantly contains unesterified retinol, experiments were conducted to determine whether membranes from the lactating mammary gland are able to synthesize retinyl esters in vitro. When microsomes from rats lactating for 7 to 14 days were incubated with [(3)H]retinol dispersed in dimethylsulfoxide, some [(3)H]retinol esterification was observed (147 pmol/5 min per 0.5 mg protein). However, 3- to 7-fold increases in retinyl ester synthesis could be achieved by supplying either a fatty acyl CoA-generating system or preformed fatty acyl CoA thioesters; thus, the major activity in vitro has the characteristics of a fatty acyl CoA: retinol acyltransferase. Both long-chain and medium-chain fatty acyl CoA esters stimulated [(3)H]-labeled retinyl ester synthesis in vitro. Concordantly, analysis of the retinyl ester pattern of rat milk demonstrated the presence of eight different esters of retinol ranging in fatty acyl chain length from 8 to 18 carbons. Retinol esterification by microsomes was maximal at neutral pH (7.1) in the presence of approximately 50 micro M palmitoyl CoA, and was linear with time of incubation for at least 5 min. Retinyl ester synthesis increased with the apparent concentration of [(3)H]retinol to approximately 200 nmol/ml, but was also dependent on the ratio of retinol relative to total microsomal protein in the incubation mixture. These experiments demonstrate for the first time retinol esterification by mammary gland membranes and point to the hypothesis that free retinol from plasma is esterified in this organ before secretion of retinyl esters in milk.-Ross, A. C., Retinol esterification by mammary gland microsomes from the lactating rat.
منابع مشابه
Retinol esterification by rat liver microsomes. Evidence for a fatty acyl coenzyme A: retinol acyltransferase.
To explore the nature of retinyl ester synthesis by liver microsomes, membranes prepared from rat or cat liver were incubated under various conditions with [3H] retinol dispersed in dimethyl sulfoxide. When [3H]retinol, buffer, and microsomes were incubated together (basal conditions), some [3H]retinol esterification was consistently observed. However, the rate of esterification could be increa...
متن کاملControl of Glucose Metabolism in Isolated Acini of the Lactating Mammary Gland of the Rat EFFECTS OF OLEATE ON GLUCOSE UTILIZATION AND LIPOGENESIS By ALISON M. ROBINSON and DERMOT
Oleate (1 mM) had only small inhibitory effects on glucose utilization and lipogenesis in acini isolated from rat mammary gland. Esterification of [1-14C]oleate was unaffected by insulin but was decreased by 60% by acetoacetate (2mM). Glycerol (1mM), but not insulin, relieved this inhibition. These experiments provide further support for the role of acetoacetate in regulating substrate utilizat...
متن کاملRetinol esterification by microsomes from the mucosa of human small intestine. Evidence for acyl-Coenzyme A retinol acyltransferase activity.
The mechanism of the intestinal esterification of retinol has been obscure. Recently, an acyl-Coenzyme A (CoA):retinol acyltransferase (ARAT) was found in rat intestinal microsomes, and experiments were therefore conducted to determine whether a corresponding enzyme exists in human small intestine. When microsomes were incubated with [3H]retinol and palmitoyl-CoA, or retinol and [1-14C]palmitoy...
متن کاملRadiation inactivation analysis of acyl-CoA:retinol acyltransferase and lecithin:retinol acyltransferase in rat liver.
Microsomes from liver and several other tissues esterify retinol through both fatty acyl-CoA-dependent and -independent reactions. Two activities, acyl-CoA:retinol acyltransferase (ARAT) and lecithin:retinol acyltransferase (LRAT) activities, have been characterized enzymatically but neither has yet been purified and characterized biochemically. We have used the method of radiation inactivation...
متن کاملEvidence for a lecithin-retinol acyltransferase activity in the rat small intestine.
Cellular retinol-binding protein, type II (CRBP (II] is an abundant protein of the mature enterocytes of the small intestine. It has been shown to direct retinol to an acyl-CoA-independent esterifying activity that utilizes an endogenous acyl donor (Ong, D.E., Kakkad, B., and MacDonald, P.N. (1987) J. Biol. Chem. 262, 2729-2736). Here we report that this activity in intestinal microsomes will c...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Journal of lipid research
دوره 23 1 شماره
صفحات -
تاریخ انتشار 1982