Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
In processes of barley plant development, various endo- and exopeptidases are involved. To determine the type and number of aminopeptidases that could participate in barley seed germination and tissue growth, their activities in extracts of non-germinated and germinated barley (Hordeum vulgare L. cv. Angora) grains and young tissues have been examined, and some of their properties determined. Aminopeptidases (AP) hydrolysing 2-naphthylamides of various amino acids were present in dry and germinated grains, roots, seedlings and leaves, showing preferences for amino acids phenylalanine (Phe), arginine (Arg), leucine (Leu) and methionine (Met), and lower activity towards alanine (Ala), proline (Pro), glycine (Gly) and histidine (His). Levels and ratios of AP activities changed during germination and tissue development, indicating that APs of different specificities are required at different stages of germination and in young tissues. Thus, the increase of all aminopeptidase activities during the first 24 hours of germination and subsequent decrease show significant involvement in seed primary metabolism restoration. The activities of Arg- and HisAP are equally important in green malt. Seedlings and leaves have pronounced substrate specificity for Phe, Leu, Ala and Pro, while roots have the lowest AP specific activities. From the activities and determined properties, the presence of at least six aminopeptidases optimally active at pH=7.4–8.2 could be discerned in dry and germinated grains, and young tissues of Angora barley. Two aminopeptidases are most probably of broad substrate specificity, three show narrow preference with dominating Leu, Phe, or Pro/His, while one is specific for Arg.U procesu klijanja ječma i razvoja nove biljke sudjeluje čitav niz različitih endo- i egzopeptidaza. Kako bi se odredio tip i broj aminopeptidaza u procesu klijanja i razvoja tkiva, u ekstraktima suhoga i klijajućeg zrna ječma (Hordeum vulgare L. cv. Angora) i ekstraktima klijanjem nastalih tkiva određivana je aktivnost aminopeptidaza, a i neke značajke aminopeptidaza. Aminopeptidaze (AP) koje hidroliziraju 2-naftilamide različitih aminokiselina u suhom i naklijalom zrnu ječma, klijanjem nastalom korjenčiću i izdanku te primarnom listu preferirale su odcjepljivanje fenilalanina (Phe), arginina (Arg), leucina (Leu) i metionina (Met), dok su aktivnosti prema alaninu (Ala), prolinu (Pro), glicinu (Gly) i histidinu (His) bile slabije. Promjene specifičnih aktivnosti i odnosa aktivnosti aminopeptidaza tijekom klijanja i razvoja tkiva ječma naznačuju da su aminopeptidaze različitih specifičnosti potrebne u različitim fazama klijanja i razvoja tkiva. Povećanje aktivnosti aminopeptidaza uočeno je tijekom prva 24 sata klijanja, nakon čega se ona smanjivala, što potvrđuje važnost tih enzima u obnovi primarnog metabolizma zrna, dok su aktivnosti Arg- i HisAP bitne i u zelenom sladu. U izdancima i primarnim listovima izražena je potreba za otcjepljivanjem Phe, Leu, Ala i Pro, dok korjenčići pokazuju najslabije specifične aktivnosti AP. Na osnovi AP aktivnosti te određenih karakteristika AP, može se pretpostaviti da suho i klijajuće zrno ječma Angora, a i tkiva nastala klijanjem, sadrže najmanje 6 različitih aminopeptidaza optimalno aktivnih pri pH=7.4-8.2. Dvije su aminopeptidaze najvjerojatnije specifične za različite supstrate, a tri za Leu, Phe ili Pro/His, dok je jedna specifična samo za Arg
