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Work is continuing in the attempt to increase knowledge of the regulation of the rate of purine synthesis in man by means of an analysis of biochemical alterations leading to purine overproduction among patients with gout. The authors are now assessing the frequency of kinetic mutations in enzymes whose alterations already have been associated with increased purine synthesis. Efforts in this regard have been rewarded by the identification of a new form of alteration leading to partial deficiency of HGPRT and a kinetic variant of PRPP synthetase with increased affinity for ribose-5-phosphate. In order to identify new forms of enzyme abnormalities associated with excessive purine synthesis, the value of a proposed classification scheme requiring measurement of PRPP and ribose-5-phosphate concentration and generation is being assessed in cultured fibroblasts. It is hoped that the results of these measurements will lead to the identification of additional kinetic variants of presently known enzyme abnormalities and will help to identify new classes of mutants in the regulation of human purine metabolism. The excessive purine synthesis that underlies the hyperuricemia of a substantial number of patients with gouty arthritis reflects alterations in the normal mechanism regulating the rate of purine nucleotide synthesis. The study of such purine "overproducers" has provided insight into the nature of this regulatory mechanism and has underscored the diversity of specific genetic and biochemical aberrations affecting it. Despite these advances, however, less than 10% of all patients with gout and excessive purine production can presently be accounted for by known enzyme abnormalities (1). Recognition that current knowledge of the regulation of the rate of purine nucleotide synthesis in man is incomplete has provided the authors impetus leading to the studies described here, which are preceded by a brief review of background.

Five cases of early-onset gouty arthritis are presented, with roentgenographic abnormalities evident in the first two decades of life. Three patients suffered from "primary" gout; classification of the other two patients was difficlut because of associated mental retardation, hypothyroidism and psoriasis. Radiographic alterations included soft-tissue masses and calcification, with typical erosive abnormalities and predilection for the hands and feet. The sacroiliac joints were abnormal in two patients.

The mutation in a young gouty male with a partial deficiency of hypoxanthine-guanine phosphoribosyltransferase has been evaluated. The serum uric acid was 11.8 mg/100 ml, and the urinary uric acid excretion was 1,279 mg/24 h. Erythrocyte hypoxanthine-guanine phosphoribosyltransferase was 34.2 nmol/h/mg, adenine phosphoribosyltransferase was 36.5 nmol/h/mg and phosphoribosylpyrophosphate was 2.6 muM. Hypoxanthine-guanine phosphoribosyltransferase from peripheral leukocytes and cultured diploid skin fibroblasts was within the normal range, but enzyme activity in rectal mucosa was below the normal range. Initial velocity studies of the normal enzyme and the mutant enzyme from erythrocytes with the substrates hypoxanthine, guanine, or phosphoribosylpyrophosphate showed that the Michaelis constants were similar. Product inhibition studies distinguished the mutant enzyme from the normal enzyme. Hyperbolic kinetics with increasing phosphoribosylpyrophosphate were converted to sigmoid kinetics by 0.2 mM GMP with the mutant enzyme but not with the normal enzyme. The mutant erythrocyte hypoxanthine-guanine phosphoribosyltransferase was inactivated normally at 80 degrees C and had a normal half-life in the peripheral circulation. The mol wt of 48,000 was similar to the normal enzyme mol wt of 47,000. With isoelectric focusing, the mutant erythrocyte enzyme had two major peaks with isoelectric pH's of 5.50 and 5.70, in contrast to the isoelectric pH's of 5.76, 5.82, and 6.02 of the normal isozymes. Isoelectric focusing of leukocyte extracts from the patient revealed the presence of the mutant enzyme. Cultured diploid fibroblasts from the propositus appeared to function normally, as shown by the inability to grow in 50-100 muM azaguanine and by the normal incorporation of [14C]hypoxanthine into nucleic acid. In contrast, erythrocytes from the patient displayed abnormal properties, including the increased synthesis of phosphoribosylphyrophosphate and elevated functional activity of orotate phosphoribosyltransferase and orotidylic decarboxylase. These unique kinetic, physical, and functional properties provide support for heterogeneous structural gene mutations in partial deficiencies of hypoxanthine-guanine phosphoribosyltransferase.

In the present discussion we have presented our views on how purine biosynthesis de novo is regulated in man. The rate of the initital step unique to purine ribonucleotide biosynthesis de novo is controlled by the intracellular concentration of PP-ribose-P and purine ribonucleotides. This critical interaction of PP-ribose-P and purine ribonucleotides may be explained by a change in the physical properties of the enzyme that catalyzes this reaction. The first branch point in the pathway, following this initial step involves the utilization of IMP. Based on an in vitro analysis of the enzymes participating directly in the two biosynthetic pathways for which IMP is a substrate, we propose that the intracellular level of GTP may be more critical than previously recognized.

1. Erythrocyte adenosine deaminase (EC 3.5.4.4) and purine nucleoside (inosine) phosphorylase (EC 2.4.1.1) were measured in 33 healthy controls and 43 primary gouty subjects. Adenosine deaminase activity in controls and gouty subjects was 0.373 plus or minus 0.108 and 0.457 plus or minus 0.140 A unit per 5-10-3 ml packed red cells per h, respectively. The difference was statistically significant (P less than 0.01). Mean adenosine deaminase: inosine phosphorylase (X10) in primary gout was also significantly higher than in controls (P less than 0.05). Inosine phosphorylase activities in the two groups were not significantly different. 2. When gouty patients were divided into two groups according to weight, normal weight gouty subjects had a higher adenosine deaminase activity and an increased ration of adenosine deaminase to inosine phosphorylase when compared with overweight patients (P less than 0.10). In two control groups divided according to the percentage overweight, such differences were not found. In the case of two gouty groups divided according to the existence of gouty heredity, tophi or renal impairment, adenosine deaminase and inosine phosphorylase activity in the two groups were not significantly different. The possible biochemical role of adenosine deaminase activity in primary gout is discussed.

A deficiency of adenine phosphoribosyltransferase (APRT) enzyme activity to approximately 40% of normal has been found in erythrocytes from a young woman aged 24 years, who had suffered from recurrent gouty arthritis since 11 years of age. She also demonstrated considerable, although asymptomatic, renal impairment with a creatinine clearance of one-third normal. Her father had suffered from gouty arthritis but had a normal APRT activity; he was obese, had a high purine intake and was a regular beer drinker. The patient's mother was asymptomatic with a normal serum urate concentration, but demonstrated a similar reduction in APRT activity to that of her daughter. Eleven other asymptomatic members of the family also demonstrated a similar reduction in APRT activity in erythrocyte lysates. The pattern of inheritance was consistent with autosomal transmission. Concentrations of phosphoribosylpyrophospate (PRPP) in erythrocytes were within normal limits both in the subjects with deficient, and in those with normal, APRT activity. Partial purification of APRT enzyme from erythrocytes of the index case did not reveal any difference from the normal enzyme as far as Michaelis constants, heat stability, or mobility in polyacrylamide gel was concerned. No primary abnormality of lipoprotein metabolism was demonstrated either in the propositus or in other members of her family. Study of urate metabolism in the propositus indicated that, although urate production was within the normal range in absolute terms, there was increased incorporation of glycine into produced urate, usually taken as one index of de novo urate production. Impaired renal excretion of urate was also shown. Although detailed study of urate metabolism has not been undertaken in other family members with APRT deficiency, no conclusive relationship has yet been demonstrated between APRT deficiency and disordered urate metabolism.

AP isoenzymes were estimated in 292 patients with locomotor diseases and in 124 healthy controls. The diagnostic usefulness of AP determination is increased by estimation of isoenzymes. Investigations were made to study the biological profile of organ specific AP activities: 1. Rheumatoid arthritis and Reiter's syndrome - the total AP and L-AP activities were increased. 2. Ankylosing spondylitis treated by physiotherapy - the total AP, B-AP and I-AP activities were increased. After drug therapy an increase occurred also in L-AP activity while I-AP activity showed no significant change. 3. Progressive OA of hip and knee showed increased levels of total AP and B-AP activities. 4. Degenerative diseases of the spine, chiefly cases of discopathy, showed significantly reduced levels of AP and B-AP activities. 5. In osteoporosis there was an increase in total AP, L-AP, B-AP and I-AP activities. 6. In the active generalised form of Paget's disease, increased levels were found of total AP, B-AP, I-AP and L-AP activities. 7. In neoplastic diseases the isoenzymes can help to reveal metastatic dissemination and thus aid preoperative evaluation. 8. In gout and hyperuricemic syndromes there was a relative increase of B-AP activity and non-significant fall of L-AP activity. Increased levels of L-AP occured in patients with gallbladder disease, after immunosuppressive therapy or after infectious hepatitis. A fall of L-AP levels was found after Corticotrophin and after intraarticular administration of Kenalog. Increased B-AP activities occurred after total hip replacement, in acute or chronic pyelonephritis and in active osteonecrosis and osteoporosis. Anabolic therapy caused a significant fale of B-AP activity to fall significantly. Reduced B-AP levels were also found after antibiotic therapy. Increased I-AP activity was found in cases of osteoporosis, and in secondary amyloidosis; reduced I-AP activity was seen in mucous colitis. The activity of I-AP is assumed to increase as a result of the changed intestinal calcium and phosphorus regulation occurring in association with the enhanced bone tissue metabolism. From this point of view an order of significance is given for the activity of bone pathology in the separate diagnostic groups of locomotor diseases.

We have reported previously two siblings with gout and uric acid lithiasis associated with excessive purine production. In the erythrocytes of these patients, phosphoribosylpyrophosphate (PRPP) synthetase exhibited resistance to feedback-inhibition by normal cell constituents such as guanosine-5'-diphosphate (GDP) and adenosine-5'-diphosphate (ADP), resulting in superactivity of the mutant enzyme and consequently in increased PRPP content and availability for nucleotide synthesis. Erythrocyte PRPP content and availability were normal in the propositus' parents, his healthy brother and three sons, and they all had normal serum level and urinary excretion of uric acid, except for the mother who was hyperuricosuric. To further characterize this mutation we studied PRPP and purine metabolism in cultured fibroblasts of the affected family. PRPP synthetase in dialyzed lysates of fibroblasts from the propositus and his mother exhibited increased specific activity, more markedly at low inorganic phosphate concentration, and decreased sensitivity to inhibition by ADP and GDP, PRPP content and availability and the rate of de novo purine nucleotide synthesis were markedly increased in the fibroblasts of the propositus and to a lesser extent in the fibroblasts of his mother but were normal in the fibroblasts of the other family members investigated. The fibroblast studies demonstrate the following sequence of abnormalities: feedback-resistance of PRPP synthetase; superactivity of this enzyme in normal physiological milieu; increased availability of PRPP; and increased de novo synthesis of purine nucleotides. The pattern of inheritance of this disorder is compatible with both an X-linked recessive and autosomal dominant traits.

The significance and importance of investigation of the synovial fluid enzymes in the main arthropathies are explanined. Tables are given for the main enzymes studied, the cell compartments of origin, and data for their values in rheumatic diseases (as reported in the literature). Stress is laid on the importance of enzymes belonging to the lysosomial compartment, both in the pathogenesis of the underlying inflammation and in the relation to anatomopathological lesions in the joints. Attention is directed to the most widely accepted hypotheses. These ten to see enzymes increases in breakdown of condrocytes, as inflammatory arthritis attributable to synoviocytes and leukocytes. A personal opinion based on prior research is also presented. Further work in this sector is urged a mean of learning more about the pathology of rheumatic diseases.

The activity of metabolic pathways involved in the formation and utilization of phosphoribosylpyrophosphate (PRPP) was studied in. The erythrocytes of 34 patients with idiopathic metabolic gout. The activities of the oxidative pentose shunt, of the hypoxanthine-guanine and adenine phosphoribosyltransferases (HGPRT, APRT) and of PRPP synthetase, as well as the rates of PRPP generation and of adenine incorporation into nucleotides were found to be normal in the erythrocytes of all these patients. Four patients with metabolic gout due to enzymatic abnormalities, two relatives with partial deficiency of HGPRT and two relatives with mutant feedback-resistant PRPP synthetase, were studied for comparison. The significance of the results is discussed in relation to postulated mechanisms for purine overproduction in metabolic gout.

Activity of hypoxanthine-guanine and adenine phosphoribosyl transferase enzymes has been assayed in erythrocytes from 10 normal adults, 37 subjects with gout, and 21 mentally retarded children with high and normal urinary uric acid:creatinine ratios. These were compared with one case of known HGPRTase deficiency. Apart from the last subject, no cases of HGPRTase deficiency were found.

In hemolyzates from red cells of two brothers with purine overproduction and gout, activity of phosphoribosylpyrophosphate synthetase is more than twofold greater than that measured in normal or other gouty individuals. The increased enzyme activity, which is also demonstrable in fibroblasts of the one patient tested, is associated with increased production of 5-phosphoribosyl-1-pyrophosphate by intact cells, an indication that the enzyme abnormality is the basis for the purine overproduction. This genetic abnormality is an example of an increased enzyme activity producing a disease state.