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Dedicated to the memory 
of the late  
Prof. Dr. Igor Kregar 
(1937–2017)
Igor Kregar, Slovenian and an internationally re-
nowned biochemist in the field of proteolysis and plant 
molecular biology, unexpectedly passed away on April 11, 
2017 in Ljubljana at the age of 79. After almost 40 years of 
conducting excellent research, teaching and mentoring of 
undergraduate and graduate students at the Jožef Stefan 
Institute and Biotechnical faculty at Ljubljana University, 
he had retired in year 1997 to enjoy his family, friends, 
travel and some hobbies.
Igor was born on September 11, 1937 in Ljubljana, 
the son of architect Rado and mother Antonija. In his fam-
ily reigned an intelectual atmosphere, which resulted in his 
broad interests for reading books, enjoying traveling, clas-
sical music, art and culture in general. Interestingly, as a 
boy he was highly motivated to read adventure novels set 
in the American Wild West written by German writer Karl 
May. Many of May‘s novels were translated into the Slove-
nian language, but unfortunately those editions were not 
accessible in our libraries after World War II for unknown 
reasons, most probably political. However, Igor did have 
access to the German editions, which stimulated him to 
learn the German language. At the same time Igor enjoyed 
competitive swimming at a local swimming pool. After 
completing high school with an excellent degree, he decid-
ed to study chemistry at the University of Ljubljana. At 
that time we first met. Soon we established a friendship 
that included my classmate Franček Gubenšek. Igor was 
one of the best students in his class. He chose organic 
chemistry for his diploma at the Faculty of Chemistry at 
Ljubljana University. Then Igor joined the Department of 
Radiobiology at the Nuclear Institute Jožef Stefan (now 
Jožef Stefan Institute) by enrolling in a master‘s degree 
program and completed his PhD dissertation in December 
1965 under the mentorship of Prof. Drago Lebez, working 
on the characterization of intracellular proteinases from 
the small intestinal mucosa of the rat. At that time intracel-
lular proteases were poorly understood. The main enzyme 
studied was an acidic hemoglobin-splitting enzyme, called 
Anson‘s enzyme in laboratory jargon after the pioneering 
protein biochemist M. L. Anson. After the lysosome orga-
nelle was discovered by C. de Duve, it became clear that 
this acid protease is a lysosomal enzyme, and in 1960 it 
was characterized and named cathepsin D. Igor and the 
author started to collaborate primarily on cathepsin D and 
also on cathepsin E soon after its discovery. This was at 
that time an almost unexplored field of research and we 
were one of the pioneering groups to work in this field.
In 1968 Igor received a Fulbright scholarship to 
study in Professor John A. Rupley‘s laboratory in the De-
partment of Chemistry at the University of Arizona, Tuc-
son, USA. Coming from Yugoslavia at that time was for 
Igor (and later for the author) a completely new world. The 
Rupley laboratory was modern and very well equipped 
with adequate funding to buy chemicals. Igor studied the 
pH dependence of lysozyme-catalyzed hydrolysis of the 
N-acetylglucosamine hexasaccharide. These kinetic exper-
iments were time consuming and required precise meas-
urements, but later resulted in a high quality publication 
(1973). Rupley was an excellent biochemist with a great 
and warm but serious personality. Not to forget, Rupley 
and his lovely wife, Ila, organized nice parties in their 
Memorial Issue
ActaChimicaSlovenica
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home, thus keeping and promoting friendly relations in 
his international laboratory. I can say as one of Rupley‘s 
postdocs that those working with him were very fortunate 
and learned to enjoy hard work and at the same time to be 
happy. Igor established many friendships in the USA, es-
pecially with Rupley‘s graduate student, Karl Kramer and 
his wife Virginia, which lasted until Igor‘s death. In 1968 
Igor joined the Kramers on a unique train trip to Mexico 
where they visited Guadalajara, Mexico City and Taxco. 
On that trip the train passed through many small Mexican 
communities, some with bullet-riddled buildings, which 
were perhaps a reflection of past political conflicts. Igor 
learned to love Mexican cuisine in part through his many 
visits to the Kramer’s apartment, where Virginia made 
mouth-watering dishes such as enchiladas, refried beans, 
flautas, green chiles and spicy meats. Upon his return to 
Yugoslavia, these experiences motivated Igor to learn how 
to replicate Mexican meals and to share them with his 
family and good friends. There was a problem, however, in 
that many of the ingredients required for Mexican cooking 
were not readily available in Yugoslavia in the 1970s. Nev-
ertheless, the Kramers were able to supply Igor with Mexi-
can food items such as masa harina, a special red chile 
powder and various types of chiles in care packages until 
he was later able to obtain them locally. 
Returning to our Department at the Institute after 
his Fulbright-sponsored study in the USA, Igor continued 
his research on cathepsins. Development of the first purifi-
cation of cathepsin D by affinity chromatography allowed 
him to obtain large quantities of the pure enzyme for nu-
merous biochemical studies including structural and de-
naturation studies. Almost at the same time an acid sul-
phydryl protease was discovered (1973) and later named 
cathepsin S. This discovery was not immediatelly recog-
nized and many believed that cathepsin S and L were iden-
tical enzymes. Ultimately, this problem was solved by iso-
lating both proteins from the same species and determining 
their amino acid sequences. Cathepsin S is involved in 
antigen processing and presentation, degradation of the 
extracellular matrix, tumor progression, cardiovascular 
disease and obesity among other roles. A new method for 
cathepsin B purification from bovine lymph nodes yielded 
sufficient enzyme for biochemical characterization. All ad-
vances in the field resulted in the Second International 
Symposium on Intracellular Protein Catabolism organized 
in Ljubljana in 1975. A brief document was prepared by 
Alan Barrett, Fred Woessner, Igor Kregar and Vito Turk, 
which highlighted all known 23 intracellular proteases. 
This modest beginning resulted finally with the establish-
ment of a new classification system and the MEROPS da-
tabase, which now includes well over 1000 peptidases 
(Handbook of Proteolytic Enzymes, N.D. Rawlings and G. 
Salvesen, Preface, Acad. Press, 2013). Igor then extended 
his research on proteases to those present in the ergot fun-
gus Claviceps purpurea and bacterium Streptomyces rimo-
sus as well as proteases and their inhibitors from plants 
such as the potato. Igor and his coworkers discovered the 
potato cysteine proteinase inhibitor gene family and char-
acterized some of the expressed recombinant proteins.
Igor was a highly respected scientist and personality. 
His research resulted in approximately 80 original research 
papers and reviews published primarily in international 
journals. He attended many domestic and international 
symposia and congresses as an invited lecturer. In parallel 
to his contributions to science, he was an excellent teacher 
and popular among many students. Most of his students 
who obtained their PhD degree under his guidance went 
on to become successful researchers and professors at dif-
ferent universities and institutes. Igor served on various 
committees at the Institute. He was also the first Secretary 
General of the Slovenian Biochemical Society (1972–1987) 
and then Secretary General of the Union of Biochemical 
Societies of Yugoslavia (1987–1992) until the collapse of 
Yugoslavia. In 1987 the 18th meeting of the Federation of 
European Biochemical Societies (FEBS) was held for the 
first time in Ljubljana, which was a great success from the 
organizational and scientific points of view. Igor contribut-
ed greatly to this success, serving as secretary of this pres-
tigious meeting with more than 1800 scientists attending 
from all over the world. For his achievements in science, 
Igor received several distinguished recognitions including 
the Yugoslav Order of Labour with Silver Wreath Award 
(1978), Slovenian Boris Kidrič Fund Award (1979) and 
Lapanje Plaque from the Slovenian Biochemical Society 
(2009).
Igor‘s remarkable wife, Anka, died several months 
after he did. He is survived by two sons, Zlato and Robert, 
three grandchildren and their families. For us and for 
those who knew him, Igor always will be remembered. His 
scientific legacy will live on.
Vito Turk
Jožef Stefan Institute