Abstract
Rat kidney contains two distinct glutaminase isoenzymes. One requires phosphate for activity; the other is phosphate-independent but is activated 15-fold by maleate. By taking advantage of differences in activators and pH optima, specific assays were devised for each isoenzyme. Their distribution was then examined in individual structures of nephrons dissected from lyophilized 20-µ sections of kidney. Enzymatic cycling, oil well, and fluorometric techniques were combined to provide sufficient sensitivity to measure the enzymes in the 5- to 50-ng samples. The distribution of the two isoenzymes is complementary. Ratios of the two activities in the different structures vary from 0.05 to 50. Phosphate-independent glutaminase activity is high only in proximal straight tubules. All other structures assayed had less than one-tenth as much activity. Phosphate-dependent glutaminase activity is high in distal straight and convoluted tubules, intermediate in proximal convoluted tubules, and low in proximal straight tubules and glomeruli. Only the phosphate-dependent glutaminase activity responds to metabolic acidosis or alkalosis and this response appears to be limited to the proximal convoluted tubules. After administration of NH4Cl for 7 days to induce acidosis the activity increased 20-fold in these tubules, whereas 7 days of NaHCO3 administration to induce alkalosis caused a 40% decrease. Neither acidosis nor alkalosis affected phosphate-independent activity in any renal structure.
Highlights
In order to obtain sufficient sensitivity, the initial incubation was carried out in a small droplet contained in an oil well [18] and the resulting glutamate was amplified by the enzymatic cycling procedure of Austin et al [26]
Properties of Isoenzymes-Pi-dependent glutaminase exhibits no activity in the absence of an activator
The two isoenzymes differ in their pH optima and K, for glutamine
Summary
Rat kidney contains two distinct glutaminase isoenzymes. One requires phosphate for activity; the other is phosphateindependent but is activated 15-fold by maleate. By taking advantage of differences in activators and pH optima, specific assays were devised for each isoenzyme Their distribution was examined in individual structures of nephrons dissected from lyophilized 20-M sections of kidney. The phosphate-dependent glutaminase activity responds to metabolic acidosis or alkalosis and this response appears to be limited to the proximal convoluted tubules. Increased potential glutaminase activity, as shown by in vitro assay, cannot be the only means for increasing ammonia synthesis during onset of acidosis, it may play an important role in maintenance of the adaptive response to an acidic diet. Intensity of stainingcanbeusedasa criterion tion of the two glutaminase isoenzymes in the various structural to divide the proximal convoluted tubulesinto populationsrepcomponents of the kidney and their response to metabolic acidosis resenting different positions along the nephron. Hue and by their diameter (30 EL)which is approximately twothirds that of the proximal convoluted tubules [21]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
