Summary:The percentage of porphyrinogens äs related to total porphyrin excretion was determined in the ! urine of healthy subjects. Acidic urines (pH 5.0 to 5.9) contained 62.9 + 10.7% (x ± s, N = 11) porphyrinogens, | whereas in neutral urines (pH 6.0 to 7.2) a somewhat lower percentage (51.2 + 15.3%, N = 11) was detected.However, there was no significant difference between the mean porphyrinogen Contents of acidic and neutral urines.Evidence was found for a previously unreported pH-dependent influence on the isomer ratios of urinary coproporphyrins I and III. Acidic urines (N = 18) from healthy subjects showed significantly higher percentages , of isomer I (27.1 + 6.4%), isomer II (2.7 ± 1.1%), and isomer IV (5.0 ± 1.3%) äs compared to respective values from neutral urines (22.2 + 5.1% isomer I, 0.6 ± 0.6% isomer II, and 1.5 + 1.3% isomer IV; N = 16, p < 0.001). Conversely, the percentage of isomer III was markedly lower in acidic urines than in neutral urines (65.1 + 7.9% vs. 75.9 + 5.4%; p < 0.001). The same relationship was confirmed in an individual subject by analysis of a series of urines (N = 13) with pH values ranging from 5.4 to 7.3. These results point to the possibiiity that the atypical coproporphyrin isomers II and IV are predominantly formed by an increased isomerization rate of coproporphyrinogens under acidic intravesical conditions.In the course of systematic investigations on the forCoproporphyrins of the series I and III are the prin-mation of the atypical coproporphyrins II and IV by cipal isomers to be excreted in human urine, whereas means of isocratic ion-pair high-performance liquid the atypical isomers II and IV are only present in chromatography (HPLC), we previously observed a small amounts (1-3). It has been suggested that stringent influence of urinary pH on the respective formation of the latter results from non-enzymatic isomer ratios (8). self-isomerization of the naturally occurring copro-Here we report our subsequent studies on the influporphyrinogens (3). Porphyrinogens are the metabol-ence of urinary pH on porphyrinogen excretion and ically active intermediates in the biosynthesis of haem. on the isomer ratios of the individual coproporphyrins They are easily oxidized to the corresponding por-I -IV. phyrins in vivo and in vitro. Both porphyrinogens and porphyrins are excreted in urine (4). The proportion of porphyrins and their reduced precursors has Materials and Methods been determined by various methods in urine of bpth individuals investigated porphyric patients (5-7) and healthy controls (7)..Spontaneous urine samples of apparently healthy persons of the laboratory staff were-used in the study. One of us (P. L.) took voluntarily part in the enforced pH shifting experiment. Acidic urines were obtained by a high intake of ascorbic acid (up to 5 g per day), whüe neutral and alkaline urines were ! ) Presented in part at the Conference "Biochemische Analytik produced after Ingestion of large doses of sodium-potassium-90", Munich, Germany. hydrogen citrate (up to 10 g per day).
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