Sentence:  Private-equity nabobs bristle at being dubbed mere financiers. Piling debt onto companies' balance-sheets is only a small part of what leveraged buy-outs are about, they insist. Improving the workings of the businesses they take over is just as core to their <WSD>calling</WSD>, if not more so. Much of their pleading is public-relations bluster. 
Meaning of the word marked with <WSD> tags:  A job or occupation.