Pneumocytes enzymes

The type II pneumocytes synthesize phosphatidylcholine in a fashion quite different from that in other cells. Most other cells synthesize phosphatidylserine from cytidine diphosphate diacylglycerol and serine. The phosphatidylserine is then decarboxylated to yield phosphatidyl ethanoiamine. The final step is the successive donation of three methyl groups via S-adenosylmethionine to form phosphatidylcholine. The pulmonary biosynthetic pathway is shown in Figure 54-2. The enzyme choline phosphotransferase forms PC directly from cytidine diphosphocholine and diacylglycerol. Phosphatidylinositol formation peaks at about 35 weeks. As PI decreases in concentration, PG begins to increase. 

By an electronmicroscopical immunogold procedure using monospecific antibodies against the enzyme, Matsuura et al. (1994) localised tetrameric carbonyl reductase within the mitochondria of the type II pneumocytes of the mouse. No significant labelling was detected over other components of the epithelial cells. 

The constitutive enzyme activity of glutathione peroxidase in pneumocytes II isolated from SPF Sprague-Dawley rats is 2830 220 units/mg DNA or 211 16 units/mg protein (Forman and Fisher 1981, 1985). 

Acid phosphatase (EC 3.1.3.2) was chiefly found in the characteristic laminated vacuoles of the type II pneumocytes of the rat (Corrin et al. 1969). Not all such vacuoles nor indeed all such cells contained the enzyme but in many, acid phosphatase reaction product formed a thin rim about the periphery of the vacuoles. The enzyme was not limited to the smaller of these cytosomes and was often present in the larger and presumably older vacuoles. Occasionally reaction product was aligned alongside or within channels of the endoplasmic reticulum. The multivesicular bodies described by Sorokin (1966) and Goldenberg et al. (1967) generally contained acid phosphatase at their periphery and between the individual vesicles. 

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