INCORPORATION OF SHORT- AND LONG-CHAIN FATTY ACIDS INTO GLYCERIDES BY LACTATING-GOAT MAMMARY TISSUE

Absence of monoacylglycerol pathway for triacylglycerol synthesis in goat mammary gland

Both subcellular fractions of lactating goat mammary gland and dispersed lactating goat mammary-gland cells were able to incorporate [U-3H]2-O-hexadecylglycerol into monoalkyl-monoacylglycerol. However, the incorporation of [U-3H]2-O-hexadecylglycerol into monoalkyl-monoacylglycerol by dispersed cells was not accompanied by incorporation of fatty acid synthesized de novo or added radiolabelled fatty acid. The result therefore shows that an active monoacylglycerol pathway does not exist in goat mammary gland.

The lactose synthetase particles of lactating bovine mammary gland. Preparation of particles with intact lactose synthetase

1. The particulate form of lactating bovine mammary lactose synthetase activity is shown to be more highly organized than previously reported. 2. A novel method of shattering frozen mammary tissue with effective cell disruption is described. 3. The apparent subcellular distribution of lactose synthetase was shown to reflect the method of homogenization. 4. After mild homogenization particles associated with a high content of intact lactose synthetase activity sedimented in the lysosome size range between 5x10(4) and 3x10(5)g-min. 5. Lactose synthetase was dissociated and solubilized by VirTis homogenization and ultrasonic treatment. The activities and behaviour of UDP-galactose hydrolase, succinate dehydrogenase, beta-glucuronidase and phosphodiesterase I were compared. 6. Inhibition of UDP-galactose hydrolase by UTP and alpha-lactalbumin was observed.

Esterification of glycerol 3-phosphate in lactating guinea-pig mammary gland

1. The presence of palmitoyl-CoA-l-glycerol 3-phosphate palmitoyltransferase (EC 2.3.1.15) has been demonstrated in a particulate fraction of mammary tissue from lactating guinea pigs. 2. Cell-free preparations also catalysed the activation of palmitate and oleate, and the conversion of enzymically formed phosphatidic acid into glycerides, in accord with the Kennedy pathway of glyceride formation. 3. The properties of the system that esterifies l-glycerol 3-phosphate were studied with respect to substrates and cofactors, and the reaction product was shown to be phosphatidic acid (1,2-diacyl glycerol 3-phosphate). 4. The extent to which newly formed phosphatidic acid was converted into glyceride in a cell-free system was dependent on the nature of the acyl donor, the concentration of subcellular particles, the time of incubation and the concentration of Mg(2+).