Liver acyl phosphatase

N3 Nassi, P., Cappugi, G., Niccoli, A. and Ramponi, G. Inhibition of horse liver acyl phosphatase by orotic acid. Physiol. Chem. Phys., 5, 109-115 (1973)... 

An accelerated breakdown of high-energy phosphate could readily explain the effect of thyroxine preincubation of canary liver mitochondria with thyroxine enhances ATP breakdown, and thyroxine increases acyl phosphatase activity in liver and muscle. The principles on which these experiments were conducted undoubtedly were sound, yet the relationship between the effect of thyroxine on high-energy phosphates and the physiological role of the hormone remains unsettled. 

Using a cell membrane preparation made from guinea pig liver cortex, Bader and Sen (1966) demonstrated that acetyl phosphate and car-bamyl phosphate were hydrolyzed at a rate dependent on K which was comparable to the Na" -I- K -dependent hydrolysis of ATP. These two hydrolytic activities were closely related with regard to monovalent cation specificity, Michaelis constants, optimal pH, and inhibition by ouabain. Accordingly, fiiey have suggested that an acyl phosphate may be a functional intermediate in the system. Other acyl phosphatases have no cation requirements and are not inhibited by Hg+. ... 

Pantothenic acid occurs in foods both in the free form and bonded to coenzyme (CoA) or acyl carrier protein (ACP) therefore hydrolysis is needed to extract it totally. Since it is degraded by acid and alkaline hydrolysis, only an enzymatic digestion can be applied. Enzyme hydrolysis with papain, diastase, clarase, takadiastase, intestinal phosphatase, pigeon liver pantetheinase, or combination of them has been used. 

The synthesis of triacylglycerol takes place in the endoplasmic reticulum (ER). In liver and adipose tissue, fatty adds in the cytosol obtained from the diet or from de novo synthesis of palmitic add become inserted into the ER membrane. The reactions are shown in Fig. 13-10. Membrane-bound acyl-CoA synthetase activates two fatty acids, and membrane-bound acyl-CoA transferase esterifies them with glycerol 3-phosphate, to form phosphatidic acid. Phosphatidic acid phosphatase releases phosphate, and in the membrane, 1,2-diacylglycerol is esterified with a third molecule of fatty acid. 

Synthesis of phosphatidylcholine. The rate-limiting reaction is that catalyzed by cytidylyltransferase (reaction 2) which appears to be active only when attached to the endoplasmic reticulum, although it is also found free in the cytosol. Cytidylyltransferase is inactivated by a cAMP-dependent protein kinase and activated by a phosphatase. Translocation to the endoplasmic reticulum can be stimulated by substrates such as fatty acyl Coenzyme A (CoA). Choline deficiency can result in deposition of triacylglycerol in liver and reduced phospholipid synthesis. Enzymes (1) choline kinase ... 

A short-term regulation mechanism for cholesterol 7a-hydroxylase activity has been investigated recently in rat liver. The enzyme appears to exist in two forms, which are interconverted by cytosolic fiictors (K12). These foctors may correspond to a protein kinase and a phosphatase, which have been proposed to regulate cholesterol 7a-hydroxylase activity by a phosphorylation (active form)-dephosphorylation (inactive form) mechanism (S9). Another enzyme utilizing cholesterol as substrate, acyl-CoA cholesterol O-acyltransferase (EC 2.3.1.26), may also be regulated in this way, while the biosynthetic enzyme, HMC-CoA reductase, is inhibited in the phosphory-lated form (SIO). Thus, short-term regulation of the concentration of un-esterified cholesterol in the liver may be achieved by coordinate control of these three key enzymes in cholesterol metabolism by reversible phosphorylation (SIO). 

Alternatively the polymer 51 carrying 0.24 meq lactosyl) (l-l)sphingosine g, chemically prepared from PAN, was sialylated in 55% yield by use of recombinant rat liver a(2-3)sialyltransferase, labeled CMP-NeuAc, and calf intestinal alkaline phosphatase [37]. Again photolysis of the 2-nitrobenzylurethane group in the sialylated polymer 52 followed by acylation with stearoyl chloride afforded the GM3 ganglioside, NeuAca(2-3)Gal)ff(l-4)Glc (l-l)Cer 53. 

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