Comparison of soluble and membrane-bound pyroglutamyl peptidase I activities in rat brain tissues in the presence of detergents

Role of central and peripheral aminopeptidase activities in the control of blood pressure: a working hypothesis

Although there is a large body of knowledge on protein synthesis, the available data on protein catabolism, although quite substantial, are still inadequate. This is due to the marked differences in the activity of proteolytic enzymes, compounded by different substrate specificities and multiple environmental factors. Understanding enzyme behavior under physiological and pathological conditions requires the identification of specific proteolytic activities, such as aminopeptidases, as able to degrade certain peptidergic hormones or neuropeptides. Another requirement is the isolation, purification and characterization of the enzymes involved. In addition, systematic studies are needed to determine each enzyme's subcellular location, tissue distribution, and the influence of environmental factors such as diurnal rhythm, age, gender, diet, cholesterol, or steroids. Central and peripheral aminopeptidases may play a role in the control of blood pressure by coordinating the effect of the different peptides of the renin-angiotensin system cascade, acting through the AT(1), AT(2), and AT(4) receptors. Our review of the available data suggests the hypothesis that cholesterol or steroids, particularly testosterone, significantly influence aminopeptidase activities, their substrate availability and consequently their functions. These observations may have relevant clinical implications for a better understanding of the pathophysiology of cardiovascular diseases, and thus for their treatment with aminopeptidase inhibitors.

Ontogeny of prolyl endopeptidase and pyroglutamyl peptidase I in rat tissues

Prolyl endopeptidase and pyroglutamyl peptidase I are enzymes which participate in the degradation of thyrotropin-releasing hormone (TRH), a hormone which is thought to play an important role in the development of organs and tissues. Here, we have characterized the ontogeny of TRH degrading enzyme activity in the brain cortex, lung, heart, kidney and liver. Overall, prolyl endopeptidase activity was found to be 2 to 5 fold higher in newborn vs. adult rat tissues, with the exception of the soluble form in the liver and the particulate form in the lung. In contrast, the developmental profile of pyroglutamyl peptidase I activity was found to be more variable and tissue dependent. These results corroborate the idea that both enzymes play important, tissue-specific roles during the development and maturation of rat organs.

Ontogeny of prolyl endopeptidase and pyroglutamyl peptidase I in rat tissues

Prolyl endopeptidase and pyroglutamyl peptidase I are enzymes which participate in the degradation of thyrotropin-releasing hormone (TRH), a hormone which is thought to play an important role in the development of organs and tissues. Here, we have characterized the ontogeny of TRH degrading enzyme activity in the brain cortex, lung, heart, kidney and liver. Overall, prolyl endopeptidase activity was found to be 2 to 5 fold higher in newborn vs. adult rat tissues, with the exception of the soluble form in the liver and the particulate form in the lung. In contrast, the developmental profile of pyroglutamyl peptidase I activity was found to be more variable and tissue dependent. These results corroborate the idea that both enzymes play important, tissue-specific roles during the development and maturation of rat organs.

Subcellular distribution of membrane-bound aminopeptidases in the human and rat brain

We evaluated the subcellular distribution of four membrane-bound aminopeptidases in the human and rat brain cortex. The particulate enzymes under study--puromycin-sensitive aminopeptidase (PSA), aminopeptidase N (APN), pyroglutamyl-peptidase I (PG I) and aspartyl-aminopeptidase (Asp-AP)--were fluorometrically measured using beta-naphthylamide derivatives. Membrane-bound aminopeptidase activity was found in all the studied subcellular fractions (myelinic, synaptosomal, mitochondrial, microsomal and nuclear fractions), although not homogenously. Human PSA showed highest activity in the microsomal fraction. APN was significantly higher in the nuclear fraction of both species, while PG I showed highest activity in the synaptosomal and myelinic fractions of the human and rat brain. The present results suggest that in addition to inactivating neuropeptides at the synaptic cleft, these enzymes may participate in other physiological processes. Moreover, these peptidases may play specific roles depending on their activity levels at the different subcellular structures where they are localized.

Pyroglutamyl peptidase I and prolyl endopeptidase in human semen: increased activity in necrozoospermia

Thyrotropin-releasing hormone (TRH) and its analogues have been reported to have important functions in human semen. In the present paper, we have characterized the activity of the TRH-degrading enzymes pyroglutamyl peptidase I and prolyl endopeptidase in the fluid and prostasomes of human semen and in subcellular fractions of the corresponding sperm. Enzymatic activities were measured fluorimetrically using beta-naphthylamine derivatives as substrate. Activity associated with both enzymes was detected in seminal fluid and in the prostasome fraction, as well as in soluble and particulate sperm subcellular fractions. Pyroglutamyl-peptidase I activity presented highest levels in the particulate sperm fraction, whereas the activity of prolyl endopeptidase was maximal in the soluble sperm fraction. In addition, we compared the activity of both enzymes in different seminal fractions in normozoospermic, fertile men and in subfertile patients with different abnormalities revealed by spermiogram analysis (astenozoospermia, necrozoospermia and teratozoospermia). The activities of pyroglutamyl peptidase I and prolyl endopeptidase in necrozoospermia were found to be higher in the corresponding soluble and particulate sperm fractions, respectively, with respect to those measured in normozoospermic semen. The results of the present study indicate that these enzymes may participate in regulating the levels of seminal TRH analogues and in mediating sperm death associated with necrozoospermia.

Effect of the disruption of body fluid balance on pyroglutamyl aminopeptidase (Type-1) in rat brain structures

The activity of soluble and membrane-bound pyroglutamyl aminopeptidase Type-1 (PAP I) was evaluated in the hypothalamus, hippocampus, thalamus, brain cortex, and pituitary gland of rats after applying certain hydromineral challenges. Compared to euhydrated rats, decreased enzyme activity was found in the hypophysis of rats deprived of water for 48 h, or rats drinking ad libitum hypertonic sodium chloride solution (2%) for 6 days or distilled water for 6 days and then submitted to acute water overload. PAP I cleaves the pGlu-amino acid bond of neuropeptides such as thyroliberin, luliberin, neurotensin, and bombesin. The decay of particulate PAP I activity may cause an increase of these pyroglutamate peptides in the whole pituitary. Although the deleterious or pro-homeostatic influence of this decay remains to be elucidated, the present data provide evidence for the involvement of this enzyme activity at this anatomical location in the water-electrolyte imbalance.

Dietary fatty acid composition affects aminopeptidase activities in the testes of mice

The autocrine/paracrine control mechanisms of local factors, such as the renin-angiotensin system and the thyrotropin-releasing hormone (TRH), seem to play a relevant role in testicular physiology. It has been proposed that dietary fat composition influences male reproductive function modifying the cholesterol-phospholipid composition of testicular plasma membranes. Modifications in the composition and physical properties of the membranes may lead to alterations in the activities of membrane-bound (M-B) enzymes. We have previously demonstrated that cholesterol and steroid hormones affect aminopeptidase (AP) activities. Dietary fatty acids with different degrees of saturation modified AP activities in the serum of mice and an olive oil supplemented diet influenced the AP activities in the testes of mice. We hypothesized that the modification of dietary fat composition may affect angiotensin- [glutamyl-AP (GluAP), aspartyl-AP (AspAP)] and TRH- [pyroglutamyl-AP (pGluAP)] degrading activities in the testis. In this study, we investigated the effect of diets supplemented with sunflower oil (SFO), fish oil (FO), olive oil (OO), lard (L) or coconut oil (CO) on soluble (Sol) and M-B GluAP, AspAP and pGluAP in mice testis, using arylamides as substrates. Sol GluAP activity did not show differences among groups. However, Sol AspAP and Sol pGluAP progressively decreased with the degree of saturation of the fatty acid used in the diet. In contrast, M-B GluAP progressively increased with the degree of saturation of the fatty acid used in the diet. For M-B AspAP activity, mice fed diets containing FO showed significantly higher levels than those fed diets containing SFO, OO and L but not those containing CO. For M-B pGluAP activity, the highest levels were observed for mice fed diets containing FO and OO. The present data suggest that the type of fat used in the diet may influence the autocrine/paracrine functions of locally synthesized angiotensin peptides and TRH in the testis, and consequently may be important in male reproductive functions.

Subcellular ontogeny of brain pyroglutamyl peptidase I

The present work studies pyroglutamyl-peptidase I activity in several subcellular fractions of the developing brain. In the synaptosomal fraction, soluble pGlu-peptidase I activity is low until postnatal Day 9 (with a peak at postnatal Day 2) and the activity increases at postnatal Day 15. In later stages there are not significant changes of synaptosomal pGlu-peptidase I activity. However, in the cytosolic fraction the activity is high from ED22 until postnatal Day 9, and afterwards decreases. The changes in the particulate fractions are generally less drastic.