Secretory vacuole

The Golgi apparatus is a system of stacked, membrane-bound, flattened sacs organized in order of decreasing breadth (see Fig. 1-6). Around this system are small vesicles (50-nm diameter and larger) these are the secretory vacuoles that contain protein that is released from the cell (see Example 1.6). 

The pathway of secretory proteins and glycoproteins (protein with attached carbohydrate) through exocrine (secretory) gland cells in which secretory vacuoles are present is well established. However, the exact pathway of exchange of the membranes between the various organelles is less clear and could be either one or a combination of both of the schemes shown in Fig. 1-7. 

In the membrane flow model of Fig. 1-7, membranes move through the cell from ER—> Golgi apparatus— secretory vacuoles— plasma membrane. In the membrane shuttle proposal, the vesicles shuttle between ER and Golgi apparatus, while secretory vacuoles shuttle back and forth between the Golgi apparatus and the plasma membrane. 

All human metzincins are secreted as proenzymes. Astacins and adamalysins are mostly activated by calcium-ion-dependent serine proteases pro-protein convertases) that meet up with their substrates in trans-Golgi and secretory vacuoles. These proenzymes are known as furin-like convertases because of their homology to a serine protease called furin and a bacterial endoprotease called subtilisin. The furin-like enzymes require calcium ions to maintain structural stability whereas other serine proteases, represented by trypsin and chymotrypsin, do not. The furin-like pro-protein convertases autocleave their own N-terminal domain propeptide (self-activate) during secretion and then convert the N-terminal domains of co-secreted metzincins. Activation cascades also occur among the... 

Histamine biosynthesis and accumulation in the secretory vacuoles of the ECL cell. Histidine is taken up and decarboxylated to histamine by HOC. The histamine is accumulated in the vacuole due to the H gradient formed by a V-type ATPase and the presence of a histamine countertransport protein in the vacuolar membrane. 

Fig. 3 Representation of matiu-e secretory gland originated from C. sativa. The separate compartments of the glandular trichome are clearly shown, and the places where THC accumulates. Black areas nuclei, V vacuole, L vesicle, P plastid, ER endoplasmic reticulum. Picture obtained from http //www.hempreport.com/issues/17/malhodyl7.html...

Secretory glycoproteins are known to move from the ER to the Golgi complex where their carbohydrate side chains are trimmed and further modified (see Palade, 1975 Tartakoff, 1980 Farquhar and Palade, 1981). In most secretory cells the proteins are then concentrated into condensing vacuoles which store the secretory proteins until they are discharged by exocytosis through a fusion reaction between the vacuolar membrane and the plasma membrane. In other secretory cells, like plasma cells, proteins are condnuously secreted and they appear to leave the Golgi complex within vesicles without being concentrated before exocytosis. 

An H+ electrochemical gradient (ApH+) provides the energy required for active transport of all classical neurotransmitters into synaptic vesicles. The Mg2+-dependent vacuolar-type H+-ATPase (V-ATPase) that produces this gradient resides on internal membranes of the secretory pathway, in particular endosomes and lysosomes (vacuole in yeast) as well as secretory vesicles (Figure 3). In terms of both structure and function, this pump resembles the F-type ATPases of bacteria, mitochondria and chloroplasts, and differs from the P-type ATPases expressed at the plasma membrane of mammalian cells (e.g., the Na+/K+-, gastric H+/K+-and muscle Ca2+-ATPases) (Forgac, 1989 Nelson, 1992). The vacuolar and F0F1... 

Mature 11S globulins are hexameric proteins that are initially assembled and transported through the secretory system as intermediate trimers. In the protein storage vacuole, the subunits of these trimers are proteolytically processed to yield... 

Fig- 12.2 Schematic view of the fungal secretory pathway. N nucleus, ER endoplasmic reticulum, V vacuole, G Golgi compartment, W cell wall filled circles protein. Arrows indicate path of protein for secretion... 

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