Microsomal membranes and

A full understanding of the role of pectin in plant development requires elucidation of the mechanisms that regulate p>ectin biosynthesis (6). Our strategy for studying the biosynthesis of HGA was to 1) establish a PGA-GalAT assay that would allow detection of synthesized HGA, 2) characterize the enzyme in microsomal membranes, 3) characterize the product synthesized by the enzyme in microsomal membranes, and 4) solubilize the enzyme and characterize the solubilized enzyme and its product. 

Dose-dependent increase in cytotoxicity by isolated brown cells Hepatopancreas had 513 mg/kg DW (vs. <50 in controls) accumulations accompanied by a significant increase in hydroperoxide and malondialdehyde contents in microsomal membranes and alterations in lipid peroxidation rates... 

A continuous sucrose gradient of the total homogenate from young rat brain and electron microscopic examination of these fractions found most of the sialyltransferase activities to be localized in smooth microsomal membrane and Golgi complex derivatives and not associated with synaptosomes. 

Previous investigations from several laboratories have demonstrated that both microsomal membranes and the cytosolic fraction from rat hver are required for the biological synthesis of cholesterol [1-4]. Specifically, the following conversions have been reported to require both microsomes and cytosol acetate to cholesterol [4] squalene to cholesterol [1] squalene-2,3-oxide to lanosterol [3] lanosterol to cholesterol [1,5] A -cholestenol to cholesterol [6] lanosterol to dihydrolanosterol [7] various 4,4-dimethyl sterols to cholesterol [8] and 7-dehydrocholesterol to cholesterol [9,10]. 

As with most mitochondrial proteins, biosynthesis occurs on micro-somes and GDH is then transported into mitochondria (79). The observed binding of GDH to phosphatidylserine, which in vivo is found in microsomal membranes, and to cardiolipin, which is found in mitochondrial membranes, has led to the suggestion, not as yet demonstrated experimentally, that these phospholipids are involved in transport (79,80). 

Protein synthesis and membrane formation in embryonic and postnatal rat liver occurs faster than in the liver of adult individuals. It was demonstrated that an increase in transferase activity coincided with an increase in hydrolase activity. However, the ratio between these two activities was not constant. This ratio increased from 0.8 (day of delivery) to 2.6 (4-7 days after delivery) and subsequently decreased to 1-2 (adult rat). These fluctuations were caused by the binding of enzyme molecules with microsomal membranes, and differences in the expression of catalytic properties were caused by the relative proportions of membrane-bound and free fractions. It was demonstrated with the aid of enzyme extractions with the nonionic detergent Triton X-100 and sodium deoxycholate (Duck-Chong and Poliak, 1973 Fig. 38). There are bacterial mutants with reduced esterase activity. In some of them esterase activity is reduced because of low levels of enzyme synthesis. Other mutants have low esterase activity due to the weakening of the association of the membrane-enzyme compound (Frehel et al., 1974). 

It has been reported that a neutral sialidase activity is associated with rat liver microsomal membranes and this activity can be released from the membranes with 0.5 M NaCl. The solubilized enzyme is indistinguishable from the cytosolic enzyme with respect to pH optima and values. Isotonic sucrose solution does not solubilize the enzyme. It appears that this enzyme may represent cytosolic enzyme which is adsorbed onto the membranes (Miyagi and Tsuiki, 1985). 

---