Insulin-like growth factor-I (IGF-I) and IGF-I receptor gene expression in the kidney of the chronically hypoinsulinemic rat and hyperinsulinemic rat.

Acute streptozotocin (STZ)-induced diabetes in rats causes a transient increase in insulin-like growth factor-I (IGF-I) in the kidney, followed by a rapid renal hypertrophy and constant renal hyperperfusion. However, renal IGF-I levels return to normal within 4 days. Thus, hyperperfusion, which is independent of renal hypertrophy of the chronically diabetic kidney, is not explained by increased renal IGF-I. We studied IGF-I and IGF-I receptor gene expression in the kidney of rats with long-standing STZ-induced diabetes. IGF-I mRNA level in the chronically diabetic kidney was approximately 50% of that in control rats, whereas IGF-I receptor mRNA was increased approximately threefold. Ten days' treatment with insulin 65 days after induction of diabetes resulted in a glucose-dependent decrease in IGF-I receptor mRNA. Chronic hyperinsulinemia with near normoglycemia did not change gene expression of either IGF-I or IGF-I receptor. The studies suggest that glucose levels per se, independent of insulin levels, play an important role in the regulation of IGF-I receptor gene expression in the chronically diabetic kidney. Furthermore, kidney hyperperfusion in chronic diabetes is coupled with the increase in IGF-I receptor mRNA, despite normal kidney IGF-I levels.

Changes in amino acid composition and protein distribution during development of human deciduous enamel.

The present study is concerned with the detailed changes in protein composition and protein distribution occurring during enamel development in the human deciduous tooth from early formation till maturation. It demonstrates that enamel development in the human tooth occurs in at least three distinct stages, forming, maturing and mature, which are generally similar to those previously identified and characterized in animal teeth. The changes in amino-acid composition and protein distribution reflect the existence of two classes of proteins, termed amelogenins and enamelins. The results show that the proportions of these two classes of enamel proteins and their constituents vary with the maturity of enamel.

Rb+ influxes differentiate between growth arrest of cells by different agents.

The effect of cell cycle on Rb+ (K+) fluxes was studied in NIH 3T3 mouse fibroblasts. Serum starvation or isoleucine deprivation resulted in cell arrest at an early G1/G0 phase, accompanied by a marked decrease in both ouabain-sensitive and ouabain-resistant Rb+ influx. On the other hand, cells arrested at late G1/G0 phase by hydroxyurea treatment have high ouabain-sensitive and ouabain-resistant Rb+ influx. Butyric acid treatment resulted in cell arrest at an early G1/G0 phase, but in contrast to serum or isoleucine starvation did not decrease Rb+ influxes. It is thus shown that quiescent cells may have Rb+ influx rates as high as that of logarithmically growing cells. The results are consistent with the hypothesis that an increased ion permeability of the cell is initiated at a critical stage in G1/G0 phase, and that butyric acid may arrest the cell beyond that stage.

Bilirubin binding and neonatal acidosis.

Plasma of neonates with severe metabolic acidosis secondary to fetal hypoxia bound less bilirubin than that of neonates without acidosis, as determined by Sephadex gel filtration. There was a significant correlation between the amount of bilirubin adsorbed by Sephadex and the base deficit. The method used ruled out any influence of plasma pH per se on binding. Our results suggest that organic anions that accumulate in the plasma of asphyxiated acidotic neonates may compete with bilirubin for binding sites on albumin.

Bilirubin binding capacity of albumin isolated from cord-blood serum is less than that from serum of adults.

As estimated by Sephadex gel filtration, the bilirubin binding capacity of albumin isolated from cord-blood serum by ion-exchange chromatography is less than that of albumin isolated from serum of adults. Albumin isolated from cord-blood serum showed increased bilirubin binding as compared with the albumin in the native serum. These findings suggest that the lower bilirubin binding capacity of serum from newborns as compared with serum from adults is a result of both an intrinsic deficiency in binding capacity of neonatal albumin and the presence of substances in neonatal serum that interfere with bilirubin binding.

Interaction of phosphate analogues with glyceraldehyde-3-phosphate dehydrogenase.

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidative phosphorylation of D-glyceraldehyde 3-phosphate. A variety of phosphonates have been shown to substitute for phosphate in this reaction [Gardner, J. H., & Byers, L. D., (1977) J. Biol. Chem. 252, 5925--5927]. The dependence of the logarithm of the equilibrium constant for the reaction on the pKa2 value of the phosphonate is characterized by a Brlnsted coefficient, betaeq, of approximately 1. This represents the sensitivity of the transfer of the phosphoglyceroyl group between the active-site sulfhydryl residue (in the acyl-enzyme intermediate) and the acyl acceptor on the basicity of the acyl acceptor. Molybdate (MoO42-) can also serve as an acyl acceptor in the glyceraldehyde-3-phosphate dehydrogenase catalyzed reaction. The second-order rate constant for the reaction with molybdate is only approximately 12 times lower than the reaction with phosphate even though the pKa2 of molybdate is 3.1 units lower than the pKa2 of phosphate. The immediate product of the molybdate reaction is the acyl molybdate, 1-molybdo-3-phosphoglycerate. The acyl molybdate, like the acyl arsenate (the immediate product of the reaction when arsenate is the acyl acceptor), is kinetically unstable. At pH 7.3 (25 degrees C), the half-life for hydrolysis of the acyl molybdate, or the acyl arsenate, is less than 2.5 s. Thus, hydrolysis of 1-molybdo- and 1-arseno-3-phosphoglycerate is at least 2000 times faster than hydrolysis of 1,3-diphosphoglycerate under the same conditions. Glyceraldehyde-3-phosphate dehydrogenase has a fairly broad specificity for acyl acceptors. Most tetrahedral oxy anions tested are substrates for the enzyme (except SO4(2-) and SeO4(2-)). Tetrahedral monoanions such as ReO4- and GeO(OH)3- are not substrates but do bind to the enzyme. These results suggest the requirement of at least one anionic site on the acyl acceptor required for binding and another anionic group on the acyl receptor required for nucleophilic attack on the acyl enzyme.

Characteristics of a photoproduct of bilirubin found in vitro and in vivo, and its effect on the bilirubin binding affinity of serum.

The 430 pigment isolated from bilirubin-albumin solutions illuminated in vitro, decreased the bilirubin binding affinity of serum. This effect was demonstrated for both tightly and loosely bound bilirubin in serum, but in albumin solutions pretreated with charcoal only the binding of loosely bound bilirubin was decreased. This finding is of importance because a similar pigment has been isolated from the body fluids of an infant with Crigler-Najjar syndrome. The production and accumulation of 430 pigment during phototherapy might decrease the binding of bilirubin to albumin in the circulation.