PMID- 3897290 OWN - NLM STAT- MEDLINE DCOM- 19851002 LR - 20181113 IS - 0021-9738 (Print) IS - 0021-9738 (Linking) VI - 76 IP - 2 DP - 1985 Aug TI - Acute intermittent porphyria: characterization of a novel mutation in the structural gene for porphobilinogen deaminase. Demonstration of noncatalytic enzyme intermediates stabilized by bound substrate. PG - 865-74 AB - To investigate the molecular pathology in acute intermittent porphyria (AIP), the nature of the defective porphobilinogen (PBG)-deaminase was determined in erythrocyte lysates from 165 AIP heterozygotes from 92 unrelated families representing 20 different ethnic or demographic groups. Immunologic and physicokinetic studies revealed the occurrence of four classes of PBG-deaminase mutations. In the majority of families studied, the amount of immunoreactive enzyme protein corresponded to the amount of enzymatic activity, indicating the absence of cross-reacting immunologic material (CRIM) produced by the mutant allele. In 78 of these CRIM-negative families (designated type 1), the affected heterozygotes had half-normal PBG-deaminase activity. In three families (designated CRIM-negative type 2), symptomatic patients had increased urinary excretion of delta-aminolevulinic acid and PBG, and normal levels of erythrocyte PBG-deaminase activity. In contrast, noncatalytic, immunoreactive protein was expressed in heterozygotes from 11 families, about one-eighth of those studied, consistent with mutations in the structural gene for PBG-deaminase. Two types of CRIM-positive mutations were identified: the type 1 mutation had a CRIM/activity ratio of approximately 1.7 and a crossed-immunoelectrophoretic profile in which all the enzyme intermediates were increased, with the B or monopyrrole-enzyme intermediate predominant (B greater than A much greater than C congruent to D greater than E). The mutation altered both the kinetic and stability properties of the noncatalytic immunoreactive enzyme protein. The second CRIM-positive mutation, type 2, had markedly increased levels of noncatalytic immunoreactive protein (CRIM/activity ratio approximately 5.7). Crossed-immunoelectrophoresis revealed markedly increased amounts of the substrate-bound intermediates, B, C, D, and E (B greater than C greater than D greater than E much greater than A). The accumulation of these noncatalytic enzyme intermediates presumably resulted from the enhanced binding and/or defective release of substrate molecules. The conformation of these enzyme-substrate intermediates apparently rendered the complexes more resistant to intraerythrocyte proteolysis. These findings provide evidence for the presence of different allelic mutations in the structural gene for PBG-deaminase and document molecular genetic heterogeneity in AIP. FAU - Desnick, R J AU - Desnick RJ FAU - Ostasiewicz, L T AU - Ostasiewicz LT FAU - Tishler, P A AU - Tishler PA FAU - Mustajoki, P AU - Mustajoki P LA - eng GR - 2 T32 HD-07105/HD/NICHD NIH HHS/United States GR - AM-26824/AM/NIADDK NIH HHS/United States PT - Journal Article PT - Research Support, Non-U.S. Gov't PT - Research Support, U.S. Gov't, P.H.S. PL - United States TA - J Clin Invest JT - The Journal of clinical investigation JID - 7802877 RN - EC 2.5.1.61 (Hydroxymethylbilane Synthase) RN - EC 3.4.- (Peptide Hydrolases) RN - EC 4.3.1.- (Ammonia-Lyases) SB - IM MH - Acute Disease MH - Alleles MH - Ammonia-Lyases/*genetics MH - Erythrocyte Aging MH - *Genes MH - Hot Temperature MH - Hydroxymethylbilane Synthase/*genetics MH - Immunoelectrophoresis, Two-Dimensional MH - Isoelectric Focusing MH - Kinetics MH - *Mutation MH - Peptide Hydrolases/metabolism MH - Porphyrias/enzymology/*genetics PMC - PMC423920 EDAT- 1985/08/01 00:00 MHDA- 1985/08/01 00:01 PMCR- 1985/08/01 CRDT- 1985/08/01 00:00 PHST- 1985/08/01 00:00 [pubmed] PHST- 1985/08/01 00:01 [medline] PHST- 1985/08/01 00:00 [entrez] PHST- 1985/08/01 00:00 [pmc-release] AID - 10.1172/JCI112044 [doi] PST - ppublish SO - J Clin Invest. 1985 Aug;76(2):865-74. doi: 10.1172/JCI112044.