In vitro degradation of angiotensin II (A-II) by human placental subcellular fractions, pregnancy sera and purified placental aminopeptidases

Abstract

Abstract. The degradation of angiotensin II (Asp1-Arg2-Val3-Tyr4-Ile5-His6-Pro7-Phe8: A-II) by human placental particulate and soluble fractions, pregnant and non-pregnant sera, and highly purified placental enzymes such as placental leucine aminopeptidase P-LAP (microsomal), retroplacental serum P-LAP (soluble), aminopeptidase A and post-proline endopeptidase, was studied by measuring liberated amino acids by high performance liquid chromatography. Placental particulate and soluble fractions degraded A-II almost completely into single amino acids. The purified P-LAP (microsomal) actively liberated five amino acids from the N-terminal. The placental particulate fraction containing P-LAP (microsomal) also actively liberated these amino acids. The purified aminopeptidase A liberated Asp1 very actively as expected. When the ratio of the velocity of liberation of each amino acid to P-LAP activity measured with leu-p-nitroanilide as a substrate was calculated, placental soluble fraction liberated Asp1 very actively, but the liberation rate of Asp1 with the purified P-LAP (soluble) was very low. Therefore it seems that the enzyme in the placental soluble fraction and pregnancy serum responsible for the Asp1 liberation is not P-LAP (soluble), but aminopeptidase A. The mixture of purified P-LAP (soluble) and aminopeptidase A showed higher liberation rate of Arg2 and Val3 than that with purified aminopeptidase A alone, demonstrating that once the N-terminal Asp1 was liberated, the P-LAP (soluble) attacks the shorter peptide (angiotension III) very actively. It was concluded that P-LAP (microsomal) together with aminopeptidase A seem to contribute greatly to the degradation of A-II in pregnant women.

Purification and Characterization of Human Placental Aminopeptidase A

“…Over the course of many years, the nature of so-called 'angiotensinase' has been stud ied [16][17][18][19]. It has been widely accepted that 'angiotensinase' is not a single enzyme but includes many enzymes such as aminopepti dase M (EC 3.4.11.2), cystine aminopepti dase (EC 3.4.11.3) and aminopeptidase A (EC 3.4.11.7).…”

“…cleaves the N-terminal Asp' of angiotensin II in vitro [19]. Furthermore, we have recently observed that AAP shows a drastic hypoten sive effect in spontaneously hypertensive rats [20].…”

Purification and Characterization of Human Placental Microsomal Aminopeptidase: Immunological Difference between Placental Microsomal Aminopeptidase and Pregnancy Serum Cystyl-Aminopeptidase

“…Recently we showed that these hor mones can be degraded with placental and pregnancy serum aminopeptidases including the present enzyme in vitro [27,28]. They may function in the intracellular protein turnover or in the metabolism of biologically active peptides in normal and pathologic conditions.…”

New insights into the importance of aminopeptidase A in hypertension

“…In turn AngI is a substrate for angiotensin-converting enzyme (ACE: EC3.4.15.1), a zinc metalloprotease that hydrolizes the carboxyl terminal dipeptide histadine-leucine (His-Leu) to form AngII [10]. AngII is converted to AngIII by APA that cleaves the aspartic acid (Asp) residue at the N-terminal [11][12][13][14]. Fig.…”