|MadSci Network: Biochemistry|
First, let me appologize for its taking so long to get a response to this question - none of the volunteers were able to find an answer, and what research I did turned up little.
To start with, let's tackle the easy parts of the question. 1) Although both chlorophyll and heme contain porphyrin, each also contains side chains that vary substantially. Beside not being able to properly coordinate a ferrous ion, chlorphyll's tail would prevent its being taken up by the hemoglobin proteins to form a functional enzyme. 2) Once heme is degraded in the liver into biliverdin, it can't be converted back to heme. Once heme degradation begins, the byproducts are expelled in the bile and urine. 3) The heme in the blood is contained in the Red Blood Cells. These cells, also called Erythrocytes, arise in the bone marrow from Reticulocytes which synthesize the porphyrin rings needed to make heme from simple precursors. In other words, any prophyrins, including functional heme, absorbed in the intestines and into the blood stream would be degraded in the liver and not used for hemoglobin.
Now for the tricky question, "how chlorophyll is absorbed through the intestinal walls." The short answer is: it's not. The evidence is somewhat indirect, but suggests that chlorophyll accumulates in the gut, and is either expelled with the rest of the waste or broken down by the intestinal flora. Examinations in cattle have demonstrated a correlation between intestinal chlorophyll content and microbial activity, which can be affected by compounds found in certain grasses. Also, some enzymes found in food plants, e.g. lutein from soybeans, actually destroy chlorophyll before it gets to the small intestines. Although these data are from cattle and not humans, their more herbivorous diets expose them to much more chlorophyll than a normal human diet - it is doubtful that our omnivorous diets are better at dealing with chlorophyll than theirs. Although there is some evidence that heme may facilitate Iron absorption in humans, it is worth repeating that any heme absorbed in the gut would be degraded by the liver before entering the general circulation, and that heme and chlorophyll are not interchangeable.
As an aside, the presence of chlorophyll in the human diet has been shown to have beneficial effects, specifically because it is not absorbed. Experiments using Chlorophyllin (CHL), a solubilized form of chlorophyll, have demonstrated that chlorophyll can help to prevent liver and colon cancers by binding carcinogens commonly associated with these cancers and preventing their absorption by the intestines. So, eating foods containing a lot chlorophyll should be part of a healthy diet, but not because the chlorophyll somehow alleviates anemia.
Try the links in the MadSci Library for more information on Biochemistry.