All of these must pass through the cell membrane. Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vescicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis.ll of these must pass through the cell membrane. Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vescicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis.
Many enzymes that occur in certain tissues are found in blood plasma at higher levels when the cancer involves that tissue. Enzymes are usually measured by determining the rate at which they convert a substrate to an end product, while most tumor markers of other types are measured by a test called an immunoassay.
High liver enzymes are one of the more frequent findings at a routine doctor visit. Potentially indicating liver damage, high liver enzymes are detected by a simple blood test. While liver enzymes are usually found in the liver, damage to this important organ causes the enzymes to leak into the bloodstream. The two liver enzymes that are the most straight-forward to test for and evaluate are aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Normal, or healthy ranges for these liver enzymes are: 1  AST = 5 to 40 units per liter of serum. 2  ALT = 7 to 56 units per liter of serum.