ABSTRACT
Maintaining retinol homeostasis and the concentration of holo-CRBP depends on retinyl ester hydrolysis in liver and in nonhepatic retinoid target tissues. Initiating in situ generation of biologically active retinoids should require unique hydrolase(s) capable of responding to specific retinoid needs via regulators of retinoid metabolism. Yet much of the retinyl ester hydrolysis work has focused on esterase activity that has total and specific dependence on not to be confused with a general need for detergent (119-124). Not only would a cholate requirement exclude a role for this activity in nonhepatic retinyl ester hydrolysis, the cholate-dependent enzyme had higher affmity and specific activity for cholesterol esters and triacylglycerol, even after partial purification (121,123). Inhibition of the cholate-dependent activity monospecifk anti-pancreatic cholesterol esterase reinforces the inference that this activity embodies general
hydrolase(s) rather than retinoid-specific hydmlases. The cholate-dependent enzyme may be cospecific with or closely related to lipases involved in the processing of chylomicron-borne lipids (125).
