<prompt> Answer this question truthfullyWhat are the two forms in which fixed H from protein and phospholipid catabolism are excreted in the urine?  <response>: <reason> What are the two forms in which fixed H from protein and phospholipid catabolism are excreted in the urine? Fixed H is excreted in the urine as titratable acid e.g. H2PO4- and NH4. 