| protoporphyrin | <biochemistry> Porphyrin ring structure lacking metal ions. The most abundant is protoporphyrin IX, the immediate precursor of hem. (18 Nov 1997) |
|---|---|
| protoporphyrin type III | 2,7,12,18-Tetramethyl-3,8-divinylporphin-13,17dipropionic acid;the principal protoporphyrin found in nature (one of 15 possible isomers), characterised by the presence of 4 methyl groups, 2 vinyl groups, and 2 propionic acid side chains; a porphyrin derivative that, with iron, forms the haem of haemoglobin and the prosthetic groups of myoglobin, catalase, cytochromes, etc. (05 Mar 2000) |
| protoporphyrinogen type III | The immediate precursor of protoporphyrin III in haem biosynthesis; elevated in cases of variegate porphyria. (05 Mar 2000) |
| protoporphyrinogen type III oxidase | A mitochondrial enzyme that uses O2 to convert protoporphyrinogen type III to protoporphyrin type III in haem biosynthesis; a deficiency of this enzyme is associated with variegate porphyria. (05 Mar 2000) |
| protoporphyrins | Porphyrins with four methyl, two vinyl, and two propionic acid side chains attached to the pyrrole rings. Protoporphyrin ix occurs in haemoglobin, myoglobin, and most of the cytochromes. (12 Dec 1998) |
| protoproteose | See: primary proteose. (05 Mar 2000) |
| protopterus | <zoology> See Komtok. Origin: NL, from Gr. First + a feather (taken to mean, fin). Source: Websters Dictionary (01 Mar 1998) |
| protosalt | <chemistry> A salt derived from a protoxide base. Origin: Proto- + salt. Source: Websters Dictionary (01 Mar 1998) |
| protosilicate | <chemistry> A silicate formed with the lowest proportion of silicic acid, or having but one atom of silicon in the molecule. Origin: Proto- + silicate. Source: Websters Dictionary (01 Mar 1998) |
| protosomite | <zoology> One of the primitive segments, or metameres, of an animal. Origin: Proto- + somite. Source: Websters Dictionary (01 Mar 1998) |
| protospore | The initial product of progressive cleavage, in which a multinucleate spore is produced. Origin: proto-+ G. Sporos, seed (05 Mar 2000) |
| protostoma | During gastrulation cells on the surface of the embryo move into the interior to form the mesoderm and endoderm. The opening formed by this invagination of cells is the blastopore. It is an opening from the archenteron, the primitive gut, to the exterior. In some animals this opening becomes the anus, whilst in others it closes up and the anus opens at the same spot or nearby. In some animals, for example chick, invagination occurs without a true blastopore and the site at which the cells move in (primitive streak) may be termed a virtual blastopore. (18 Nov 1997) |
| protostome | Synonym: blastopore. Origin: proto-+ G. Stoma, mouth (05 Mar 2000) |
| Protostrongylus rufescens | The small lungworm of sheep, goats, and deer that occurs in the smaller bronchioles, where it causes plugging of the air passages by its presence and the formation of multiple areas of bronchopneumonia; symptoms produced generally are milder than those induced by the large lungworm, Dictyocaulus filaria. Origin: proto-+ G. Strongylos, round (05 Mar 2000) |
| protosulfate | A compound of sulfuric acid with a protoxide of the metal. (05 Mar 2000) |