TY - JOUR
T1 - Fatty acyl CoA-dependent and -independent retinol esterification by rat liver and lactating mammary gland microsomes
AU - Randolph, R. Keith
AU - Winkler, K. Elise
AU - Ross, A. Catharine
N1 - Funding Information:
i This work was supported by National Institutes of Health Grants HD-16484, HL-22633, HL-07443 and The Howard Heinz Endowment. * To whom correspondence and reprint requests should be addressed at: Department of Physiology and Biochemistry, Medical College of Pennsylvania, 3300 Henry Avenue, Philadelphia, PA 19129. FAX: (215) 843-8849.
PY - 1991/8/1
Y1 - 1991/8/1
N2 - Retinol esterification was examined in microsomes from rat liver and lactating mammary gland as a function of the form of retinol substrate, dependence on fatty acyl CoA, and sensitivity to phenylmethylsulfonyl fluoride (PMSF). Retinol bound to cellular retinol-binding protein (CRBP) or dispersed in solvent was esterified in a fatty acyl CoA-independent, PMSF-sensitive reaction, consistent with lecithin:retinol acyltransferase (LRAT) activity. LRAT activity exhibited the same Km (2 μm retinol) between tissues but a higher Vmax in liver as compared to that in mammary gland (47 vs 8 pmol/min/mg microsome protein, respectively). Solvent-dispersed retinol was also esterifled in a fatty acyl CoA-dependent, PMSF-resistant reaction, consistent with acyl CoA:retinol acyltransferase (ARAT) activity. Retinol bound to CRBP was not a good substrate for this reaction. ARAT activity displayed a similar Vmax (300 pmol/min/mg microsome protein) between tissues but Km values of 15 and 5 μm for retinol and fatty acyl CoA in mammary gland as compared to 30 and 25 μm, respectively, in the liver. Thus, when substrate was near or below Km, retinol esterification occurred predominantly by LRAT in the liver and ARAT in the mammary gland, respectively. The concentration of CRBP in the cytosol, determined by Western blotting, was approximately 2 μm in the liver but was almost nondetectable in the mammary gland. These data suggest that retinol esteriflcation is regulated via different mechanisms in liver and mammary gland and support a specific role for CRBP in the liver.
AB - Retinol esterification was examined in microsomes from rat liver and lactating mammary gland as a function of the form of retinol substrate, dependence on fatty acyl CoA, and sensitivity to phenylmethylsulfonyl fluoride (PMSF). Retinol bound to cellular retinol-binding protein (CRBP) or dispersed in solvent was esterified in a fatty acyl CoA-independent, PMSF-sensitive reaction, consistent with lecithin:retinol acyltransferase (LRAT) activity. LRAT activity exhibited the same Km (2 μm retinol) between tissues but a higher Vmax in liver as compared to that in mammary gland (47 vs 8 pmol/min/mg microsome protein, respectively). Solvent-dispersed retinol was also esterifled in a fatty acyl CoA-dependent, PMSF-resistant reaction, consistent with acyl CoA:retinol acyltransferase (ARAT) activity. Retinol bound to CRBP was not a good substrate for this reaction. ARAT activity displayed a similar Vmax (300 pmol/min/mg microsome protein) between tissues but Km values of 15 and 5 μm for retinol and fatty acyl CoA in mammary gland as compared to 30 and 25 μm, respectively, in the liver. Thus, when substrate was near or below Km, retinol esterification occurred predominantly by LRAT in the liver and ARAT in the mammary gland, respectively. The concentration of CRBP in the cytosol, determined by Western blotting, was approximately 2 μm in the liver but was almost nondetectable in the mammary gland. These data suggest that retinol esteriflcation is regulated via different mechanisms in liver and mammary gland and support a specific role for CRBP in the liver.
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U2 - 10.1016/0003-9861(91)90227-A
DO - 10.1016/0003-9861(91)90227-A
M3 - Article
C2 - 1898045
AN - SCOPUS:0025816991
SN - 0003-9861
VL - 288
SP - 500
EP - 508
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 2
ER -